Magnetic recording medium

ABSTRACT

In a magnetic recording medium wherein a metal thin film magnetic layer and an overcoat are formed on a nonmagnetic substrate, durability is improved when the overcoat comprises a plasma-polymerized film and a topcoat of an organic fluorine compound; a plasma-polymerized film, a protective carbon film, and a topcoat of an organic fluorine compound; a plasma-polymerized film containing C, F and H; or a plasma-polymerized organometallic film and a fluorine or silicon-containing topcoat. Oxidation of the upper surface of the magnetic layer with a plasma is also effective.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to copending application Ser. No. 943,329 filed Dec.19, 1986, Maruta et al, for Magnetic Recording Medium, Ser. No. 868,511filed May 30, 1986, Ueda et al, for Magnetic Recording Medium, Ser. No.033,617 filed Apr. 3, 1987, Yokoyama et al, for Magnetic RecordingMedium, and Ser. No. 041,489 filed Apr. 23, 1987, Yokoyama et al, forMagnetic Recording Medium, where all the applications are assigned tothe same assignee as the present invention and incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic recording medium, and moreparticularly, to an improvement in the durability of a magneticrecording medium of the hard type such as magnetic disks and drums.

Magnetic recording media used in cooperation with magnetic diskapparatus are generally known as magnetic disks or disk media and havethe basic structure comprising an annular substrate having a magneticlayer usually on each of its surfaces.

The materials of which the substrates of such magnetic recording mediaare made include two types, hard materials such as aluminum alloy andplastic materials such as Mylar as also used in magnetic tape media. Ingeneral, the former is called a magnetic disk of the hard type and thelatter a flexible disk.

The magnetic recording media for use with magnetic disk or drumapparatus, particularly hard type magnetic disks encounter some problemsof durability and abrasion resistance against mechanical contact with amagnetic head. To this end, magnetic recording media are usuallyprovided with a protective coat. Known as the protective coat of suchmedia are protective films of inorganic material and lubricating filmsof solid lubricant.

The inorganic protective films used in the prior art are formed from,for example, Rh and Cr as disclosed in Japanese Patent Publication No.52-18001, Ni-P as disclosed in Japanese Patent Publication No. 54-33726,Re, Os, Ru, Ag, Au, Cu, Pt and Pd as disclosed in Japanese PatentPublication No. 57-6177, and Ni-Cr as disclosed in Japanese PatentPublication No. 57-17292. The commonly used solid lubricants areinorganic and organic lubricants including silicon compounds such asSiO₂, SiO, and Si₂ N₄ as disclosed in Japanese Patent Publication No.54-33726, polysilicic acid and silane coupling agents such astetrahydroxysilane and polyaminosilane as disclosed in Japanese PatentPublication No. 59-39809, and carbon.

The conventional protective films formed on the magnetic layer fromthese materials are somewhat unsuccessful in enhancing the durability,abrasion resistance, weatherability, and corrosion resistance of theassociated media and suffer from the phenomenon called grip that thehead adheres to the medium surface.

In our copending application Ser. No. 943,329 filed Dec. 19, 1986, weproposed a combination of a topcoat layer and a protective carbon filmon a magnetic recording medium, the topcoat layer comprised of anorganic fluorine compound of the same type as used in the presentinvention and characterized by improvements in durability, abrasionresistance, weatherability, corrosion resistance and grip resistance. Inour copending application Ser. No. 033,617 filed Apr. 3, 1987, directedto a similar magnetic recording medium, the topcoat layer is formed froman organic fluorine compound by gas phase deposition.

Also, in our copending application Ser. No. 868,511 filed May 30, 1986,we proposed a topcoat layer for a magnetic tape having a metal magneticthin film layer, the topcoat layer being formed from a fluorocarbonresin by sputtering or ion plating.

In general, the disk medium has the structure wherein various necessarylayers including primary, magnetic, and intermediate layers are disposedone on top of the other on a substrate. The durability of medium havingsuch a layered structure depends on not only the nature of a protectivelayer disposed on the top surface of the medium, but also the adhesionor bond strength between the respective layers. A defective bond betweenany two layers will lead to a loss of the overall medium durability.There is the need for further improving the overall durability ofmagnetic recording medium.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel and improvedmagnetic recording medium having excellent durability, abrasionresistance, weatherability, and corrosion resistance as well asincreased reliability in practical applications.

The present invention is generally directed to a magnetic recordingmedium comprising a nonmagnetic substrate having opposed major surfaces,a metal thin film magnetic layer on one major surface of the substrate,and a topcoat layer on the magnetic layer.

According to a first aspect of the present invention, there is provideda magnetic recording medium comprising

a nonmagnetic substrate having opposed major surfaces,

a metal thin film magnetic layer on one major surface of the substrate,

a plasma-polymerized film on the magnetic layer, and

a topcoat layer comprising an organic fluorine compound on theplasma-polymerized film.

Preferably, a protective film of carbon is interposed between theplasma-polymerized film and the topcoat layer.

According to a second aspect of the present invention, there is provideda magnetic recording medium comprising

a nonmagnetic substrate having opposed major surfaces,

a metal thin film magnetic layer disposed on one major surface of thesubstrate, and

a topcoat layer on the magnetic layer, said topcoat layer comprising aplasma-polymerized film containing carbon, fluoride, and optionally,hydrogen, the carbon content ranging from 30 to 80 atom %.

Preferably, the surface of the magnetic layer remote from the substrateis oxidized, typically with a plasma.

According to a third aspect of the present invention, there is provideda magnetic recording medium comprising

a nonmagnetic substrate having opposed major surfaces,

a metal thin film magnetic layer on one major surface of the substrate,

a plasma-polymerized film of an organometallic compound on the magneticlayer, and

a topcoat layer on the plasma-polymerized film.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more fully understood by reading the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1 to 3 are schematic cross-sectional views of magnetic recordingmedia according to some preferred embodiments of the present invention.

FIG. 4 is a schematic view of a plasma polymerizing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIRST EMBODIMENT

Referring to FIG. 1, there is illustrated in cross section a magneticrecording medium generally indicated at 1 according to a first preferredembodiment of the present invention. The magnetic recording medium 1includes a nonmagnetic substrate 2 having opposed major surfaces forcarrying a necessary number of layers thereon. In the broadest sense, onthe substrate 2, an undercoat layer 3, an intermediate layer 4 of anonmagnetic metal, a metal thin film magnetic layer 5, a protectivelayer 6 of a nonmagnetic metal, a protective carbon film 8, and atopcoat layer 9 are disposed one on top of the other in this order.Additionally in the illustrated embodiment, plasma-polymerized films 71and 75 are disposed just below and above the protective carbon film 8,respectively. Although the two plasma-polymerized films are provided, atleast one plasma-polymerized film suffices for the present invention.The plasma-polymerized film may be disposed contiguous to the protectivenonmagnetic metal film 6 or the magnetic layer 5 if the film 6 isabsent.

One layer has a pair of opposed surfaces, the upper surface remote fromthe substrate and the lower surface adjacent to the substrate. In mostcases, the term surface used herein in conjunction with a layer or filmrepresents the upper surface of the layer or film located remote fromthe substrate unless otherwise stated.

Plasma-Polymerized Film

The plasma-polymerized films 71 and 75 formed just below and above theprotective carbon film 8 according to the present invention are eachcomprised of a thin plasma-polymerized film consisting essentially ofcarbon and hydrogen.

The film is prepared by activating a gaseous monomeric reactant into aplasma for plasma polymerization. Exemplary of the gaseous monomersthere may be given saturated and unsaturated hydrocarbons, for example,methane, ethane, propane, butane, pentane, ethylene, propylene, butene,butadiene, acetylene, methylacetylene, and the like and mixturesthereof. Preferably, they are gaseous at room temperature because ofease of operation. If desired, a hydrocarbon which is liquid at roomtemperature may be used as the reactant for plasma polymerization.Useful reactant gas is a mixture of at least one of the hydrocarbons andat least one inorganic gas selected from H₂, O₂, O₃, H₂ O, N₂, NO_(x)including NO, N₂ O and NO₂, NH₃, CO, and CO₂. The reactant mayoptionally contain a minor proportion of silicon, boron, phosphorus,sulfur, etc.

The plasma-polymerized film is formed from such a reactant to athickness of 3 to 300 Å. Thicknesses in excess of 300 Å undesirablyincrease the spacing loss (magnetic loss due to thickness component).Thicknesses of less than 3 Å are too thin to provide the observableeffect. The film thickness may be measured by means of an ellipsometer.Control of film thickness in forming a plasma-polymerized film may bedone by a choice of reaction time, reactant gas flow rate and otherfactors.

The plasma-polymerized film may be prepared on a subject by using theabove-mentioned hydrocarbon as a gaseous monomeric reactant, creating adischarge plasma of the reactant, and contacting the plasma with thesubject.

The principle of plasma polymerization will be briefly described. Whenan electric field is applied to a gas kept at a reduced pressure, freeelectrons which are present in a minor proportion in the gas and have aremarkably greater inter-molecular distance than under atmosphericpressure are accelerated under the electric field to gain a kineticenergy (electron temperature) of 5 to 10 eV. These accelerated electronscollide against atoms and molecules to fracture their atomic andmolecular orbitals to thereby dissociate them into normally unstablechemical species such as electrons, ions, neutral radicals, etc. Thedissociated electrons are again accelerated under the electric field todissociate further atoms and molecules. This chain reaction causes thegas to be instantaneously converted into highly ionized state. This isgenerally called a plasma. Since gaseous molecules have a less chance ofcollision with electrons and absorb little energy, they are kept at atemperature approximate to room temperature. Such a system in which thekinetic energy (electron temperature) of electrons and the thermalmotion (gas temperature) of molecules are not correlated is designated alow temperature plasma. In this system, chemical species set up thestate capable of additive chemical reaction such as polymerization whilebeing kept relatively unchanged from the original. The present inventionutilizes this state to form a plasma-polymerized film on a subject, forexample, the protective carbon film carried on the substrate. The use ofa low temperature plasma avoids any thermal influence on the subjectincluding any previously deposited layers and the substrate.

FIG. 4 illustrates a typical apparatus in which a plasma-polymerizedfilm is formed on the surface of a subject. This plasma-polymerizingapparatus uses a variable frequency power source. The apparatuscomprises a reactor vessel R into which a gaseous reactant or reactantsare introduced from a source 511 and/or 512 through a mass flowcontroller 521 and/or 522. When desired, different gases from thesources 511 and 512 may be mixed in a mixer 53 to introduce a gasmixture into the reactor vessel. The reactant gases may be fed each at aflow rate of 1 to 250 ml per minute.

Disposed in the reactor vessel R are a pair of opposed electrodes 551and 552. One electrode 552 is a rotary support electrode on which asubject 111 to be treaeed rests. The subject 111 is placed between theelectrodes 551 and 552. The electrode 551 is connected to a variablefrequency power source 54 and the rotary support electrode 552 groundedat 8. Although the coated substrate to be treated is supported on theelectrode in the reactor vessel in the illustrated embodiment,continuous operation can be made by continuously moving a length ofsubstrate along the electrode, if desired.

The reactor vessel R is further connected to a vacuum system forevacuating the vessel, including an oil rotary vacuum pump 56, aliquefied nitrogen trap 57, an oil diffusion pump 58, and a vacuumcontroller 59. The vacuum system has the capacity of evacuating andkeeping the reactor vessel R at a vacuum of 0.01 to 10 Torr.

In operation, the reactor vessel R is first evacuated by means of thevacuum pump to a vacuum of 10⁻³ Torr or lower before a reactant gas orgases are fed into the vessel at a predetermined flow rate. Then theinterior of the reactor vessel is maintained at a vacuum of 0.01 to 10Torr. When the flow rate of the reactant gas becomes constant, thevariable frequency power 54 is turned on to generate a plasma with whichthe reactant is polymerized to form a plasma-polymerized film on thesubject 111.

For plasma polymerization, a carrier gas such as argon, helium, nitrogenand hydrogen may be used.

The frequency of the power source is not critical to the plasmatreatment according to the present invention. The source may be of DC,AC, and microwave in addition to the high-frequency electric dischargeas mentioned above.

Preferably, the plasma-polymerized film is prepared by feeding a gaseousreactant into a plasma zone with W/F.M set to at least 10⁷ joule/kgwhere W is an input power applied for plasma generation as expressed injoule/sec., F is a flow rate of the reactant gas as expressed inkg/sec., and M is the molecular weight of the reactant. If W/F.M is lessthan 10⁷, the resulting plasma-polymerized film is insufficiently denseto exert the desired effect. The upper limit of parameter W/F.M isgenerally about 10¹⁵ joule/kg.

The remaining parameters such as applied current and operating time maybe as usual and properly chosen without undue experimentation.

The plasma-polymerized film prepared as above preferably contains 30 to100 atom %, more preferably 30 to 80 atom % of carbon. Preferably theplasma-polymerized film contains carbon and hydrogen in an atomic ratioof carbon to hydrogen (C/H) in the range of from 1:1 to 6:1. Aplasma-polymerized film having such a C/H ratio exhibits outstandinglyimproved corrosion resistance and durability. C/H ratios of less than 1provide films practically unacceptable in corrosion resistance,durability and strength. A substantial reduction in output occurs afterrepeated passes at C/H ratios of higher than 6.

The plasma-polymerized film may further contain up to 20 atom % of N, O,Si, B, P, or S, or a mixture thereof. Preferably, the plasma-polymerizedfilm contains nitrogen and/or oxygen in a total amount of 2 to 40 atom%, especially 10 to 30 atom % because of improved low-temperature CSScharacteristics.

It should be noted that the C/H and other atom ratios may be determinedby SIMS (secondary ion mass spectroscopy), for example. When SIMS isused, the C/H ratio of the present plasma-polymerized film having athickness of 3 to 300 A may be calculated by determining the counts of Cand H at the film surface. Alternatively, the C/H ratio may becalculated by determining the profile of C and H while effecting ionetching with Ar or the like. The measurement of SIMS may be in accordwith the article "SIMS and LAMMA" in the Surface Science Basic Lectures,Vol. 3, 1984, Elementary and Application of Surface Analysis, page 70.

Plasma Treatment

Preferably, in the preparation of the magnetic recording medium 1 shownin FIG. 1 according to the first embodiment of the present invention,any one or all of the surfaces of the magnetic layer 5, the protectivenonmagnetic metal film 6, and the protective carbon film 8 may bepretreated with a plasma before the plasma-polymerized films 71, 75 areformed. The plasma treatment of the surface of a layer increases thestrength of bond between the layer and a subsequently applied layer,eventually contributing to improved durability of the medium.

The principle, procedure and conditions of plasma treatment areessentially the same as previously described for the plasmapolymerization. It is to be understood that the plasma treatment uses,in principle, an inorganic gas as the treating gas whereas the plasmapolymerization uses an organic reactant gas, optionally in admixturewith an inorganic gas, to form a plasma-polymerized film.

The identity of gas is not critical to the plasma treatment. That is,the treating atmosphere used in the plasma treatment is not particularlylimited. The atmosphere may be comprised of an inorganic gas selectedfrom air, H₂, Ar, He, O₂, O₃, H₂ O, N₂, NH₃, and NO_(x) including NO, N₂O, and NO₂, and mixtures thereof.

The frequency of the power source is not critical to the plasmatreatment according to the present invention. The source may be of DC,AC, and microwave. It is to be noted that other parameters includingsupply current and treating time may be as usual or properly selectedwithout undue experimentation.

As previously described, the plasma-polymerized film is formed on theupper and/or lower surface of the protective carbon film 8. When theplasma-polymerized film 71 is present below the protective carbon film8, the plasma-polymerized film is formed on the magnetic layer 5directly or via the protective nonmagnetic metal film 6 as illustrated,and thereafter the protective carbon film is deposited. If desired ornecessary, another plasma-polymerized film 75 may be formed on theprotective carbon film. The provision of the plasma-polymerized films71, 75 significantly improves the durability, abrasion resistance,weatherability, and corrosion resistance of the overall medium.

Topcoat Layer

According to the first embodiment of the present invention, the topcoatlayer 9 is disposed directly on the plasma-polymerized film 75 or on theprotective carbon film 8 when the film 75 is absent. The topcoat layeris formed from an organic fluorine compound as the uppermost layer ofthe medium. The organic fluorine compound is preferably selected fromthe group consisting of (A) carboxyperfluoropolyethers and salts andesters thereof, (B) perfluoropolyethers, (C) tetrafluoroethylenepolymers, and (D) other fluorocarbon resins.

(A) Carboxyperfluoropolyethers, Salts and Esters

In a first example, the topcoat layer contains acarboxyperfluoropolyether or a salt or ester thereof.

The perfluoropolyethers are perfluoro deviratives of polyalkylethers.The carboxyperfluoropolyethers are those perfluoropolyethers having acarboxylic acid radical or its salt substituted at their end. The numberof carboxylic acid radicals is not particularly limited, but ispreferably 1 or 2.

Typical carboxyperfluoropolyethers, salts, and esters used herein arecompounds having the general formula (I):

    Rf--(--Rf'O--).sub.n --Rf"COOR1                            (I)

wherein Rf represents a fluorine atom, a perfluoroalkyl radical, --COOZ,or --ORf"COOZ;

Rf' and Rf" are independently selected from divalent perfluoroalkyleneradicals and may be the same or different;

n is a positive integer, with the proviso that when n is 2 or more, acorresponding plurality of Rf' may be the same or different;

R1 represents hydrogen, a monovalent cation, or a substituted orunsubstituted alkyl radical; and

Z has the same meaning as R1, with the proviso that Z and R1 in formula(I) may be the same or different.

Examples of the perfluoroalkyl radicals represented by Rf include --CF₃,--C₂ F₅, --C₃ F₇, etc. Examples of perfluoroalkylene radicalsrepresented by Rf' and Rf" include --CF₂ --, --CF₂ CF₂ --, ##STR1##etc., with --CF₂ --, --CF₂ CF₂ --, and --CF(CF₃)--CF₂ -- beingpreferred.

Preferred examples of Rf are --F, --COOCH₃, --COOH, --COOC₂ H₅, and--COOC₃ H₇.

Examples of the substituted or unsubstituted alkyl represented by R1include --CH₃, --C₂ H₅, --C₃ H₇, i--C₃ H₇, --C₄ H₉, and --C₅ H₁₁. R1 ispreferably selected from unsubstituted alkyl radicals having 1 to 5carbon atoms, more preferably --CH₃ and --C₂ H₅.

Examples of the cations represented by R1 include alkali metal cationssuch as Na⁺, K⁺, and Li⁺, and NH₄ ⁺.

The letter n generally ranges from about 10 to about 100, preferablyfrom 30 to 70.

When more than one Rf' is present, they may be the same or different.

The esters having formula (I) may be either carboxylic acid monoester ordiesters.

Preferred among the compounds of formula (I) are those compounds havingthe general formulae: ##STR2## wherein Z and R1 are as defined informula (I), the sum of m and p is the same as n defined in formula (I).Preferably Z and R1 are H and --CH₃, and each of m and p generallyranges from 5 to 50, preferably from 5 to 20.

Another preferred class includes those compounds

having the general formulae: ##STR3## wherein R1 and n are as defined informula (I). Preferably R1 is H, --CH₃ or --C₂ H₅, and n generallyranges from 10 to 100, preferably from 30 to 70.

These compounds have a molecular weight of about 1,000 to 10,000.

These compounds may be readily synthesized by a conventional knownmethod and are commercially available.

Typical examples of commercial products of these compounds are KRYTOX157FS manufactured by E.I. DuPont which corresponds to the compounds offormula (I-3) wherein R1 is H and n is 11 to 49, FOMBLIN Z DIACmanufactured by Montefluos which corresponds to the compounds of formula(I-2), and FOMBLIN Z DEAL manufactured by Montefluos which correspondsto the compounds of formula (I-1) wherein Z and R1 are methyl, and m andp are 11 to 49.

(B) Perfluoropolyethers

In a second example, the topcoat layer contains a perfluoropolyether.

Typical perfluoropolyethers used herein are compounds having the generalformula (II):

    R2f--(--R2f'O--).sub.n --R2f"                              (II)

wherein R2f represents a fluorine atom or a perfluoroalkyl radical; R2f'is a perfluoroalkylene radical; R2f" is a perfluoroalkyl radical; and nis a positive integer. When R2f is a perfluoroalkyl radical, R2f andR2f" may be the same or different. When n is 2 or more, a correspondingplurality of R2f' may be the same or different.

Examples of the perfluoroalkyl radicals represented by R2f include--CF₃, --C₂ F₅, etc. Preferably, R2f is --F or --CF₃. Examples ofperfluoroalkylene radicals represented by R2f' include --CF₂ --, --CF₂CF₂ --, ##STR4## etc., Examples of the perfluoroalkyl radicalsrepresented by R2f" include --CF₃, --C₂ F₅, etc.

The letter n generally ranges from about 10 to about 100, preferablyfrom 10 to 50.

Preferred among the compounds of formula (II) are those compounds havingthe general formulae (II-1) and (II-2): ##STR5## wherein the sum of mand p is about 10 to 100. Each of m and p generally ranges from 5 to 50,preferably from 5 to 30.

Another preferred class includes those compounds having the generalformula (II-3): ##STR6## wherein n is as defined in formula (II). Theletter n generally ranges from 10 to 100, preferably from 30 to 70.

These compounds have an average molecular weight of about 1,000 to10,000.

These compounds may be readily synthesized by a conventional knownmethod and are commercially available.

Typical examples of commercial products of these compounds are FOMBLINY04, Y06, Y25, Y45, YR; FOMBLIN Y-L-VAC0616, Y-L-VAC 14/6, Y-L-VAC 16/6,Y-L-VAC 25/6; FOMBLIN Y-H-VAC 18/8, Y-H-VAC 25/9, Y-H-VAC 40/11, Y-H-VAC140/13; and FOMBLIN Z, all manufactured by Montefluos Company; andKRYTOX 143CZ, 143AZ, 143AA, 143AY, 143AB, 143AC, 143AD, KRYTOX 1502,1504, 1506, 1509, 1514, 1516, 1525, 1618, 1625, 1645, 1680, and 1614,all manufactured by E.I. DuPont. Among them, KRYTOX 143CZ corresponds tothe compounds of formula (II-3) wherein n is 11 to 49, and FOMBLIN Y andZ correspond to formulae (II-2) and (II-1), respectively.

(C) Tetrafluoroethylene Polymers

In a third embodiment, the topcoat layer contains a tetrafluoroethylenepolymer preferably having a molecular weight of 1,000 to 10,000.

The polymers preferably have a softening point of about 200° to 300° C.as measured according to ASTM E-28-58T and a melting point of about 200°to 350° C.

These polymers may be readily synthesized by a conventional well-knownmethod and commercially available.

Typical examples of commercially available products of thetetrafluoroethylene polymers are Vydax A12, 5100, 550, and 525manufactured by E.I. DuPont and AG-LUB manufactured by Asahi Glass K.K.

(D) Fluorocarbon Resins

In a fourth example, the topcoat layer contains a fluorocarbon resin.

Typical fluorocarbon resins used herein include polyvinylidene fluoride(PVdF), polyvinyl fluoride (PVF),tetrafluoroethylene-hexafluoropropylene copolymers (FEP),tetrafluoroethylene-ethlylene copolymers (ETFE),tetrafluoroethylene-perfluoroalkylvinyl ether copolymers (PFA),chlorotrifluoroethylene-ethylene copolymers (ECTFE), etc. propylenecopolymers (FEP) and tetrafluoroethylene-hexafluoropropylene copolymers(ETFE). The fluorocarbon resins preferably have an average degree ofpolymerization of about 700 to 3,000.

The compounds (A) to (D) may be present alone or as a mixture of two ormore in the topcoat layer 9.

The total content of these fluorine comounds ranges from 50 to 100% byweight, preferably from 70 to 100% by weight based on the weight of thetopcoat layer 9. Less than 50% by weight of the fluorine compoundimparts insufficient lubricity to the topcoat.

Any other materials may be present in the topcoat layer 9. Preferredexamples of the additional materials are fatty acids, fatty acid esters,epoxy resins, and phenolic resins.

The topcoat layer 9 may be formed by any desired methods includingsolvent deposition and gas phase deposition.

The solvent deposition includes spin coating, dipping and spray coating,for example. The coating solution used herein is usually prepared byadding 0.01 to 1.0% by weight, preferably 0.05 to 0.1% by weight of oneor more of compounds (A) to (D), especially compounds (A) and (B) tofluorine solvent, typically Fron.

Coating conditions may be readily determined by those skilled in the artwithout undue experimentation. Spin coating favors 500 to 3,000revolutions per minute and a spinning time of about 5 to 20 seconds.Dipping may be carried out by immersing a sample in a Fron or similarsolvent for about 15 to 30 seconds for cleaning, then immersing in thecoating solution for about 10 to 30 seconds, and pulling up at a speedof about 5 to 20 mm/second.

The gas phase deposition processes include evaporation, sputtering andion plating. The solids component of compounds (A) to (D) may be used asa source for gas phase deposition. A mixture of two or more of compounds(A) to (D) may be present in the topcoat layer as previously described.

The gas phase deposition has the features that a thin deposit can beformed to a uniform thickness and no organic solvent is contained in thetopcoat deposited. Therefore, the topcoat formed by gas phase depositionhas various advantages including a uniform thickness, and less frequentgrip by a head and low friction, all promising improved performance inactual operation.

The evaporation, sputtering and ion plating methods will be described indetail as typical gas phase deposition. Any of these methods may beutilized in the present invention although the use of vacuum depositionor sputtering is preferred.

First, the evaporation or vacuum deposition is a method wherein anevaporation source is melted and evaporated by heating in a highlyevacuated atmosphere at about 10⁻³ Torr or lower by electron beam,resistance heating and the like. The resulting vapor is deposited, forexample, on the substrate surface to form a thin film. The vaporparticles are imparted with a kinetic energy of about 0.1 to 1 eV uponevaporation.

Next, the sputtering process will be described. The sputtering processmay be further classified into plasma sputtering and ion beam sputteringdepending on the region where operation is conducted.

In the plasma sputtering process, an abnormal glow discharge isgenerated in an atmosphere of an inert gas such as argon, a target ofsource material to be evaporated is sputtered with the resulting Arions, and the thus generated vapor of source material is deposited orcondensed on the substrate. Included are a DC sputtering techniquewherein a DC voltage of several kilovolts is applied and a highfrequency sputtering technique wherein a high frequency power of severalto several hundred kilowatts is applied. A magnetron type sputteringtechnique is also useful wherein a multi-pole sputtering equipment suchas two, three or four pole sputtering equipment is used, andelectromagnetic fields are applied in two perpendicular directions toimpart a cycloidal motion to electrons in the plasma, as by a magnetron,to form a high density plasma, thereby reducing the voltage applied andimproving the sputtering efficiency. If desired, instead of a pure inertgas atmosphere such as argon, there may be used reactive or chemicalsputtering using an atmosphere containing an active gas such as O₂ andN₂ in admixture with argon.

In the ion beam sputtering process, a suitable ionization source likeargon (Ar) is ionized. The ionized Ar is driven out as an ion beam in ahigh vacuum by applying a negative high voltage across drivingelectrodes. The ion beam is impinged on the surface of a target ofsource material to be evaporated. The resulting vapor of source materialis deposited or condensed on the substrate.

In either sputtering process, the operating pressure is about 10⁻² to10⁻³ Torr

These sputtering processes impart particles of source material with akinetic energy of about several eV (electron volts) to about 100 eVwhich is substantially greater than the kinetic energy of about 0.1 eVto about 1 eV given by the evaporation processes.

Further, the ion plating process is an atomistic film forming processwherein evaporated material ions having a sufficient kinetic energy arebombarded on the surface of a substrate before and during formation of afilm thereon. The basic functions involved are sputtering, heating andion implantation of the substrate by bombarding ions, which affect theadherence, nucleation and growth of a film being deposited. The ionplating process may be further classified into plasma and ion beamprocesses depending on the region where operation is carried out.

In the plasma ion plating process, a substrate held at a negativepotential is cleaned by impinging Ar⁺ or similar cations thereon under aDC glow discharge, and an evaporation source is then heated to evaporatethe source material which is ionized in the plasma. The resulting sourcematerial ions are accelerated under an electric field of increasedintensity in a cathodic dark region of the glow discharge surroundingthe substrate and then bombarded on the substrate with a high energy,whereby the material deposits on the substrate. Any techniques of plasmaion plating may be employed including DC application, high frequencyexcitation, and their combination, and their combination with variousheating modes of the evaporation source. A plasma electron beamtechnique using a hollow cathode plasma electron gun may also beemployed.

In the ion beam plating process, a source material is converted intoions by any ion producing means including sputtering, electronbombardment, or modified duo-plasmatron equipment. The resulting vaporof source material ions is driven out into a high vacuum region under acontrolled accelerating voltage to successively carry out cleaning anddeposition on the surface of a substrate. A cluster ion beam techniquefor evaporation and crystal growth may also be employed wherein a jet ofsource material is injected from a crucible into a high vacuum throughan injection nozzle to form a cluster containing 10² to 10³ looselycombined atoms by utilizing an overcooling phenomenon due to adiabaticexpansion.

The kinetic energy imparted to ions by ion plating is in the range offrom about several ten eV to about 5000 eV, which is greatly higher thanthat given by dry coating processes, for example, evaporation process(about 0.1 eV to about 1 eV) and sputtering process (about several eV toabout 100 eV). For this reason, the film deposited by ion platingexhibits an outstandingly increased adherence. An increased rate ofdeposition completes film formation within a short time.

A recently developed arc discharge ion plating technique involvingthermionic ionization may also be used. The arc discharge ion platingtechnique includes heating an evaporation source to form a stream ofvapor, impinging electrons emitted from a thermionic emission sourceagainst the vapor stream at a position near tee evaporation source wherethe vapor stream is relatively dense, thereby ionizing the vapor stream,and focusing the ionized vapor stream under an electric or magneticfield at a substrate in a direction perpendicular thereto.

In these gas phase deposition processes, conditions such as substratetemperature, substrate-to-hearth or target distance and the like may beas usual.

The topcoat layer 9 may be formed by either coating or gas phasedeposition as described above. Generally, the topcoat layer thus formedhas a thickness of from 3 to 300 Å, preferably from 5 to 150 Å. Athickness of less than 3 Å fails to provide the benefits of theinvention, particularly durability. Topcoat layers having a thickness inexcess of 300 Å are liable to grip, giving rise to so-called head crush.

Protective Carbon Film

The topcoat layer 9 and the second plasma-polymerized film 75 may beformed on the protective carbon film 8. The protective carbon film 8 hasa composition consisting essentially of carbon although the compositionmay contain less than 5% by weight of another element.

The protective carbon film 8 may be formed by any gas-phase depositiontechniques including sputtering, ion plating, evaporation, and chemicalvapor deposition (CVD). Among them sputtering is most preferred becausethere is produced a very coherent dense film which is effective indurability and weatherability improvements.

The protective carbon film 8 generally has a thickness of 10 to 800 Å,preferably 100 to 400 Å.

Preferably, the protective carbon film 8 is plasma treated at itssurface prior to subsequent covering with the topcoat layer. The plasmatreatment chemically activates the surface of the protective carbon film8 so that the second plasma-polymerized film 75 or the topcoat layer 9may be more firmly bonded thereto. The bond strength between theadjoining layers is then increased, offering significantly increaseddurability. The plasma treatment may be carried out as previouslydescribed.

Substrate

The nonmagnetic substrate 2 used in the practice of the presentinvention is usually rigid one and may be made of such materials asmetals, for example, aluminum and aluminum alloys, glass, ceramics, andengineering plastics. Aluminum and aluminum alloys are preferred amongthem because of their mechanical rigidity, workability, and bond to theundercoat layer.

The nonmagnetic substrate 2 generally has a thickness of about 1.2 toabout 1.9 mm and a shape of disk or drum although no particular limit isimposed on the thickness and shape.

Undercoat

Particularly when the nonmagnetic substrate 2 is a rigid metalsubstrate, typically aluminum or aluminum alloy, it is preferred to formthe undercoat layer 3 on the substrate. The undercoat layer 3 may have acomposition of Ni-P, Ni-Cu-P, Ni-W-P, Ni-B or the like. It may be formedby liquid phase plating, particularly electroless plating. Theelectroless plating produces a very dense film having increasedmechanical rigidity, hardness, and processability.

More specifically, the compositions of the undercoat layer may berepresented by the formulae:

(Ni_(x) Cu_(y))_(A) P_(B) and (Ni_(x) W_(y))_(A) P_(B),

wherein x:y=100:0 to 10:90, and

A:B=97:3 to 85:15 in weight ratio.

The Ni-B compositions are represented by the formula: Ni_(x) B_(y)wherein x:y=97:3 to 90:10.

One exemplary process of the electroless plating involves alkalinedegreasing, acidic degreasing, several cycles of zincate treatment,surface adjustment with sodium bicarbonate or similar agents, andsubsequent plating in a nickel electroless plating bath at pH 4.0 to 6.0at a temperature of about 80° to 95° C. for about 1/2 to about 3 hours.For further detail of the chemical plating, reference is made toJapanese Patent Publication Nos. 48-18842 and 50-1438.

The undercoat layer 3 has a thickness of about 3 to 50 μm, preferablyabout 5 to 20 μm.

In a further preferred embodiment, the undercoat layer 3 is providedwith irregularities at the surface. To impart an irregular surface tothe undercoat layer 3 on the disk-shaped substrate 2, abrasive is causedto act on the surface of the undercoat layer 3 while rotating thesubstrate, thereby forming irregular grooves on the undercoat surface ina concentric pattern. Alternatively, the irregularities may be randomlyprovided on the undercoat layer 3. The provision of irregularitiesresults in improved properties of grip and durability.

When the undercoat layer 3 is absent, the substrate 2 may be directlyprovided with such irregularities on its surface.

Magnetic Layer

On the substrate 2 optionally having the undercoat layer 3 is formed themetal thin film magnetic layer 5 comprising cobalt or a major proportionof cobalt and at least one of nickel, chromium, and phosphorus.

Illustrative examples of the composition of the metal thin film areCo-Ni, Co-Ni-Cr, Co-Cr, Co-Ni-P, Co-Zn-P, Co-Ni-Mn-Re-P, etc. Mostpreferred among them are Co-Ni, Co-Ni-Cr, Co-Cr, and Co-Ni-P. Thesealloys have the preferred compositions of

Co-Ni having a proportion of Co:Ni between 1:1 and 9:1 in weight ratio;

(Co_(x) Ni_(y))_(A) Cr_(B) wherein x:y=1:1 to 9:1 and A:B=99.9:0.1 to75:25;

Co-Cr having a proportion of Co:Cr=7:3 to 9:1; and (Co_(x) Ni_(y))_(A)P_(B) wherein x:y=1:0 to 1:9 and A:B=99.9:0.1 to 85:15. Recordingproperties decline outside these ranges.

These metal thin film magnetic layer 5 may be formed by any desired gasand liquid phase plating techniques. Sputtering, one of gas phaseplating as described above, is preferred because there are producedmagnetic layers having favorable magnetic properties.

The material of the target used herein is an alloy or metal mixturecorresponding to the composition of the desired metal thin film magneticlayer 5.

When the metal thin film magnetic layer 5 has a composition of CoP orCoNiP, liquid phase plating methods, inter alia, electroless plating maybe employed. Magnetic layers obtained by liquid phase plating alsoexhibit as good magnetic properties as those obtained by sputtering.

The bath composition and operating parameters used in the electrolessplating are known and any suitable combination thereof may be usedherein, as disclosed in Japanese Patent Publication Nos. 54-9136 and55-14865.

The metal thin film magnetic layer 5 generally has a thickness of 200 to5,000 Å, and preferably 500 to 1,000 Å.

Intermediate Layer

When the metal thin film magnetic layer 5 is formed by sputtering asdescribed above, it is preferred to interpose a nonmagnetic metalintermediate layer 4 containing Cr between the undercoat layer 3 and themagnetic layer 5. The provision of the nonmagnetic metal intermediatelayer 4 contributes to improvements in magnetic properties andreliability of recording properties of the medium. Most preferably thenonmagnetic metal intermediate layer 4 consists of Cr although a Crcontent of at least 99% by weight is acceptable.

The intermediate layer 4 may be formed by any of various known gas phasefilm forming methods. Usually, it is preferred to form the intermediatelayer by sputtering a in the metal thin film magnetic layer 5 describedabove. The thickness of the nonmagnetic metal intermediate layer 4generally ranges from about 500 to about 4,000 Å although it depends onthe type of the metal thin film magnetic layer 5.

Protective Nonmagnetic Metal Film

The magnetic recording medium 1 of the present invention preferably hasa protective nonmagnetic metal film 6 of Cr or similar metal interposedbetween the metal thin film magnetic layer 5 and the protective carbonfilm 8 (or the first plasma-polymerized film 71 when it is present belowthe carbon film 8). The provision of the protective nonmagnetic metalfilm 6 significantly improves the durability and weatherability of theresulting magnetic recording medium. Most preferably, the protectivenonmagnetic metal film 6 consists of Cr although a Cr content of atleast 99% by weight is acceptable.

The protective nonmagnetic metal film 6 may be formed by any of knowngas phase deposition processes, and usually it is preferable to form theprotective film by sputtering. The protective nonmagnetic metal film 6generally has a thickness of about 30 to 300 Å, preferably about 50 to200 Å.

SECOND EMBODIMENT

Referring to FIG. 2, there is illustrated in cross section a magneticrecording medium generally indicated at 1 according to one preferredembodiment of the second aspect of the present invention. The magneticrecording medium 1 includes a nonmagnetic substrate 2 having opposedmajor surfaces for carrying a necessary number of layers thereon. Ingeneral on the substrate 2, an undercoat layer 3, an intermediate layer4 of a nonmagnetic metal, a metal thin film magnetic layer 5, aprotective layer 6 of a nonmagnetic metal, a protective carbon film 8,and a topcoat layer 9 are disposed one on top of the other in thisorder.

Topcoat Layer

The topcoat layer 9 in this embodiment is a thin plasma-polymerized filmcontaining carbon and fluorine, or carbon, fluorine, and hydrogen.

The thin film containing these elements may be formed by activating agaseous monomeric reactant into a plasma for plasma polymerization.Exemplary of the gaseous monomers there may be given fluorocarbons suchas tetrafluoromethane, octafluoroproppane, octafluorocyclobutane,tetrafluoroethylene, hexafluoropropylene, etc., and fluorinatedhydrocarbons such as fluoromethane, difluoromethane, trifluoromethane,difluoroethane, tetrafluoroethane, etc., and mixtures thereof.Preferably, they are gaseous at room temperature because of ease ofoperation.

In admixture with the above-mentioned reactant, there may also be usedsaturated and unsaturated hydrocarbons, for example, methane, ethane,propane, butane, pentane, ethylene, propylene, butene, butadiene,acetylene, methylacetylene, etc. and mixtures thereof. Another fluoridesuch as boron fluoride, nitrogen fluoride, and silicon fluoride may alsobe used as one component of the reactant gas feed in admixture with thefluorine-containing reactant mentioned above. Also, fluorine-containingmaterials which are liquid or solid at room temperature, for example,Freon 12, Freon 13B1 and Freon 22, may also be used as a reactant ifdesired or necessary.

The reactant gas feed may optionally contain a minor proportion ofnitrogen, oxygen, silicon, boron, phosphorus, etc. Then the topcoat filmcontains a minor proportion of such an element.

The carbon content of the topcoat film ranges from 30 to 80 atom %, morepreferably from 30 to 60 atom %. Dynamic friction increases with carboncontents in excess of 80 atom % whereas carbon contents of less than 30atom % detract from runnability.

In the preferred topcoat film, the atomic ratio of hydrogen to fluorine(H/F) ranges from 0.1 to 1.1, more preferably from 0.9 to 0.9:1. Dynamicfriction increases with H/F ratios of more than 1.

The topcoat film preferably contains carbon and fluorine at an atomicratio of fluorine to carbon (F/C) in the range from 0.3:1 to 2:1, morepreferably from 0.5:1 to 1.5:1. A satisfactory loss of dynamic frictionis not expected at a F/C ratio of less than 0.3:1. A F/C ratio of morethan 2:1 results in a considerable output reduction with increasingpasses.

Where the topcoat film contains carbon, fluorine, and hydrogen, theatomic ratio of carbon to hydrogen (C/H) ranges from 2:1 to 8:1,preferably from 2.5:1 to 5:1. A C/H ratio of less than 2:1 isinsufficient to ensure corrosion resistance whereas a C/H ratio inexcess of 8:1 detracts from durability. The atomic ratio of hydrogen tofluorine (H/F) preferably ranges from 0.2:1 to 1:1, more preferably from0.2:1 to 0.9:1. H/F ratios of less than 0.2:1 provide less satisfactorydurability. Initial friction becomes too high with H/F ratios of morethan 1:1.

In one preferred embodiment, the topcoat film is formed such that theatomic ratio of fluorine to carbon (F/C) increases toward the surface ofthe film. More illustratively, in the plasma-polymerized topcoat film,the average F/C atom ratio in the upper region of the film that extendsfrom the surface remote from the substrate to 1/3rd of its thickness isat least 1.5 times, more preferably at least twice that in the lowerregion of the film that extends from the surface adjacent to thesubstrate to 1/3rd of its thickness. The topcoat film having such agradient or distribution of fluorine concentration generally containscarbon, fluorine, and hydrogen, provided that the contents of carbon andthe remaining elements in the entire film are within the above-definedrange.

More preferably, the average F/C atom ratio in the upper 1/3 region ofthe film ranges from 1.5:1 to 3.0:1 whereas the average F/C atom ratioin the lower 1/3 region of the film ranges from 1.0:1 to 1.5:1, with theratio of the former to the latter being at least 1.5:1. The presence ofa fluorine rich surface region in the topcoat film increases thedurability of the medium. The distribution of fluorine and carbon may beeither continuous or discontinuous as long as the above-mentionedgradient is imparted. Such a graded distribution can be accomplished bycontrolling the composition of the plasma reactant gas feed with thelapse of time.

Elemental analysis of F/C in the topcoat film may be carried out by anyconventional techniques such as SIMS, ESCA, and Auger spectroscopy. Theprocedure of SIMS is as previously described.

The plasma-polymerized film topcoat has a thickness of 3 to 800 Å. Athickness in excess of 800 Å results in an undesirably increased spacingloss. Less than 3 Å fails to provide the benefits of the invention. Itis to be noted that the thickness of the plasma-polymerized filmpreferably ranges from 3 to 300 Å where the protective carbon film isinterposed between the magnetic layer and the topcoat layer as will bedescribed later.

Preferably, the topcoat layer has a contact angle with water in therange from 100° to 130°, more preferably from 10° to 125°. Topcoatlayers having a contact angle of less than 100° exhibit a higher initialfriction and are unacceptable for actual utility. Plasma-polymerizedfilms having a contact angle of more than 130° are difficult to form andunnecessary for most applications.

The film thickness may be measured by means of an ellipsometer and canbe controlled by a choice of the reaction time, feed gas flow rate andother factors during film formation by plasma polymerization.

Preferably, the plasma-polymerized film is prepared by feeding a gaseousreactant into a plasma zone with W/(F.M) set to at least 10⁷ joule/kgwhere W is an input power applied for plasma generation as expressed injoule/sec., F is a flow rate of the reactant gas as expressed inkg/sec., and M is the molecular weight of the reactant. If W/F.M is lessthan 10⁷, the resulting plasma-polymerized film is insufficiently denseto provide the desired corrosion resistance. The upper limit ofparameter W/F.M is generally about 10¹⁵ joule/kg. It is to be noted thatwhen more than one reactant is used, F and M are the sum of them.

The reactant gases may be fed each at a flow rate of 1 to 250 ml perminute.

In operation, the reactor vessel R (see FIG. 4) is first evacuated bymeans of the vacuum pump to a vacuum of 10⁻³ Torr or lower before areactant gas or gases are fed into the vessel at a predetermined flowrate. Then the interior of the reactor vessel is maintained at a vacuumof 0.01 to 10 Torr. When the flow rate of the reactant gas becomesconstant, the variable frequency power is turned on to generate a plasmawith which the reactant is polymerized to form a plasma-polymerized filmon the subject.

For plasma polymerization, a carrier gas such as argon, helium, nitrogenand hydrogen may be used.

The frequency of the power source is not critical to the plasmatreatment according to the present invention. The source may be of DC,AC, and microwave as well as high-frequency discharge. Current supplyand treating time may be as usual.

The topcoat film 9 is most preferably formed on the protective carbonfilm 8, but may be on the surface of the protective nonmagnetic metalfilm 6 when the carbon film 8 is omitted as understood from FIG. 2.

As in the first embodiment, the surface of the protective carbon filmmay preferably be pretreated with a plasma. Plasma treatment chemicalactivates the surface of the protective carbon film so that theplasma-polymerized film or topcoat may be subsequently formed thereon invery firm adherence. For the same reason, it is effective toplasma-treat the surface of any layer on which the protective carbonfilm 7 is formed, for example, the protective nonmagnetic metal film 6.

Also preferably in the second embodiment, the protective nonmagneticmetal film 6 is interposed between the metal thin film magnetic layer 5and the protective carbon film 8.

Magnetic Layer

The magnetic layer 5 used herein comprises a major proportion of cobaltand oxygen, or cobalt, oxygen and at least one member selected fromnickel, chromium and phosphorus. Preferably, oxygen is introduced in themagnetic layer mainly by plasma oxidizing the magnetic layer surface aswill be described later.

In the magnetic layer, the average atomic ratio of oxygen to cobalt(O/Co) preferably ranges from 0.01:1 to 0.3:1, more preferably from0.01:1 to 0.2:1. Atomic ratios O/Co of more than 0.3:1 lead todeterioration in rectangular ratio known as one of magnetic parameters.The effect of this embodiment is not exerted with atomic ratios of lessthan 0.01:1.

Most preferably, the average atomic ratio of oxygen to cobalt in theregion of the magnetic layer that extends from its surface remote fromthe substrate to a level of 1/10th of its thickness is at least 3 times,especially at least 5 times the average atomic ratio of oxygen to cobaltin the region of the magnetic layer that extends from its surfaceadjacent to the substrate to a level of 1/10th of its thickness. Outsidethis range, durability, abrasion resistance, and weatherability are lessimproved.

The magnetic layer of the above-mentioned organization may be formed byfirst depositing a thin film comprised predominantly of Co or Co plusNi, Cr and/or P on a substrate usually via an undercoat layer by anysuitable methods such as sputtering and plating. The thin film is thenoxidized to introduce oxygen into a surface region where oxygen formsoxides with ferromagnetic cobalt and optional metal. In a surfaceregion, particularly a surface region extending from the surface remotefrom the substrate to a depth of 100 Å, more preferably to a depth of 50Å, a peak indicative of oxide is observed by Auger spectroscopy.

The oxidizing treatment used herein is plasma oxidation. The use ofplasma oxidation enables on-line treatment and uniform oxidation toachieve stable oxidation treatment, forming a dense oxidized film. Thereare additional benefits of elimination of chemical liquid and lowtemperature treatment. Plasma oxidation may be carried out by using anoxidizing gas as a treating gas, activating the gas into a electricdischarge plasma, and contacting the plasma with the surface of a thinfilm of Co-Ni or similar ferromagnetic metal or alloy. As a result ofplasma oxidation, the medium is remarkably improved in durability,abrasion resistance, weatherability, and corrosion resistance.

The principle of plasma oxidation is essentially the same as thatpreviously described in conjunction with the plasma treatment and plasmapolymerization. A low-temperature plasma is utilized in this case too.Plasma oxidation may be practiced using the apparatus as shown in FIG.4.

In operation, the reactor vessel R is first evacuated by means of thevacuum pump to a vacuum of 10⁻³ Torr or lower before a treating gas orgases are fed into the vessel at a predetermined flow rate of 1 to 250ml per minute. Then the interior of the reactor vessel is maintained ata vacuum of 0.01 to 10 Torr. When the flow rate of the treating gasbecomes constant, the variable frequency power is turned on to generatea plasma with which the subject is oxidized.

The treating gas used in plasma oxidation may be at least one oxidizinggas selected from air, O₂, O₃, H₂ O, CO, CO₂, and NO_(x) including NOand NO₂, and mixtures thereof. An inorganic gas such as nitrogen, argon,helium and neon may additionally be used in combination with theoxidizing gas.

The frequency of the power source is not critical to the plasmatreatment according to the present invention. The source may be of DC,AC, high frequency, and microwave. Other parameters including supplycurrent and treating time may be as usual or properly selected withoutundue experimentation.

The metal thin film magnetic layer has a thickness of 200 to 5,000 Å,preferably 500 to 1,000 Å.

Before plasma oxidation, the metal thin film magnetic layer has achemical composition predominantly comprising cobalt or cobalt plus atleast one of nickel, chromium and phosphorus as previously described inthe first embodiment.

On the magnetic layer 5 whose surface is plasma oxidized, a topcoatlayer 9 as defined above may be formed with or without any desiredintervening layers

With respect to the nonmagnetic substrate 2, undercoat layer 3, andintermediate nonmagnetic metal layer 4, the same as previously describedin conjunction with the first embodiment also applies to the secondembodiment including material, preparation, surface processing and otherparameters.

Further, a protective film 6 of a nonmagnetic metal such as chromium maybe formed between the metal thin film magnetic layer 5 and the topcoat 9as previously described in conjunction with the first embodiment. Aprotective carbon layer 8 may preferably formed on the protectivenonmagnetic metal film 6. The protective carbon layer applied in thepreferred embodiment has a thickness of 10 to 800 Å, more preferably 100to 400 Å. Also the surfaces of the protective nonmagnetic metal film 6and the protective carbon film 7 may be plasma treated as in thepreceding embodiments. The plasma treatment enhances the bond betweenthe treated layer and the overlying layer, resulting in media havingimproved durability. The plasma treatment may be carried out aspreviously described.

THIRD EMBODIMENT

Referring to FIG. 3, the magnetic recording medium 1 according to thethird embodiment of the present invention includes a nonmagneticsubstrate 2 having opposed major surfaces for carrying a necessarynumber of layers thereon. In general on the substrate 2, an undercoatlayer 3, an intermediate layer 4 of a nonmagnetic metal, a metal thinfilm magnetic layer 5, a protective layer 7 of a plasma-polymerizedorganometallic compound, a protective film 8 of carbon, and a topcoatlayer 9 of a plasma-polymerized fluorine or silicon compound aredisposed one on top of the other in this order.

Plasma-Polymerized Organometallic Film

The protective layer 8 of plasma-polymerized organometallic compound maybe formed by creating an electric discharge plasma of a carrier gas suchas argon (Ar), helium (He), hydrogen (H₂) and nitrogen (N₂), introducingan organometallic compound in vapor form or vapor of a solution of anorganometallic compound in a organic solvent into the discharge plasma,and contacting the activated gaseous mixture with the surface of asubject to be treated. The subject to be treated is a substrate having amagnetic layer already formed thereon in this embodiment. Theorgano-metallic compound used herein may be selected from organiccompounds and organic complex salts of tin, titanium, aluminum, cobalt,iron, copper, nickel, manganese, zinc, lead, galium, indium, mercury,magnesium, selenium, arsenic, gold, silver, cadmium, germanium, etc. aslong as they can be plasma polymerized.

Illustrative of the organometallic compounds are those having formulae(A), (B), (C), (D), (E), and (F). In the formulae, M is a metal, I to VIattached to M represent the valence of the metal, R is an organoradical, X is hydrogen or halogen.

(A) M^(I) R

Examples are phenyl copper and phenyl silver.

(B) M^(II) R_(p) X_(2-p)

In formula (B), p is equal to 1 or 2. Examples of the compounds offormula (B) include diethyl zinc, dimethyl zinc, methyl iodide mercury,methyl iodide magnesium, ethyl bromide magnesium, dimethyl mercury,dimethyl selenium, dimethyl magnesium, diethyl magnesium, diphenylmagnesium, dimethyl zinc, di-n-propyl zinc, di-n-butyl zinc, diphenylzinc, diphenyl cadmium, diethyl mercury, di-n-propyl mercury, allylethyl mercury, and diphenyl mercury.

(C) M^(III) R_(q) X_(3-q)

In formula (C), q is equal to 1, 2 or 3. Examples of the compounds offormula (C) include trimethylaluminum, triethylaluminum,triisobutylaluminum, trimethylgallium, trimethylindium, diethyl aluminumchloride, and trimethylgold.

(D) M^(IV) R_(r) X_(4-r)

In formula (D), r is equal to 1, 2, 3 or 4. Examples of the compounds offormula (D) include tetramethyltin, di-n-butyl tin maleate, dibutyl tindiacetate, tetra-n-butyltin, tetraethyllead, tetramethyl germane,tetraethyl germane, diethylcyclogermanahexane, tetraphenyl germane,methyl germane, ethyl germane, n-propyl germane, triethyl germane,diphenyl germane, triphenyl germane, trimethyl bromogermane, triethylbromogermane, triethyl fluorogermane, triethyl chlorogermane, dimethyldichlorogermane, methyl trichlorogermane, diethyl dichlorogermane,diethyl dibromogermane, diphenyl dibromogermane, diphenyldichlorogermane, ethyl trichlorogermane, ethyl tribromogermane, n-propyltrichlorogermane, tetraethyltin, trimethylethyltin, tetraallyltin,tetraphenyltin, phenyltrimethyltin, triphenylmethyltin, dimethyldichloride tin, dimethyl tin dihydride, trimethyl tin hydride, triphenyltin hydride, tetramethyllead, tetra-n-propyllead, tetraisopropyllead,trimethylethyllead, trimethyl-n-propyllead, and dimethyldiethyllead.

(E) M^(VI) R_(6-s)

In formula (E), s is equal to 1, 2, 3, 4 or 6. Examples of the compoundsof formula (E) include hexaethyl germane, hexamethyl ditin, hexaethylditin, and hexaphenyl ditin.

(F) Acetylacetone complex salts

Examples are titanium acetylacetonate, aluminum acetylacetonate, cobaltacetylacetonate, iron acetylacetonate, copper acetylacetonate, nickelacetylacetonate, and manganese acetylacetonate.

In the formulae, R is an organic radical selected from alkyl having 1 to10 carbon atoms, preferably alkyl having 1 to 6 carbon atoms, alkenylhaving 2 to 6 carbon atoms, preferably allyl, aryl, preferably phenyl,and acyloxy, preferably maleoyl and acetyl; and X is hydrogen or halogenincluding fluorine, chlorine, bromine and iodine. Also included arephenylarsine oxide and analogs.

The plasma polymerization technique used herein is by creating anelectric discharge plasma of a carrier gas such as argon (Ar), helium(He), hydrogen (H₂) and nitrogen (N₂), introducing an organometallicmonomer into the discharge plasma, and contacting the activated gaseousmixture with the surface of a subject to be treated, thereby forming aplasma-polymerized film on the surface.

The principle of plasma polymerization is already described in the firstembodiment. The reagents may be fed each at a flow rate of 1 to 250 mlper minute.

In operation, the reactor vessel R (see FIG. 4) is first evacuated bymeans of the vacuum pump to a vacuum of 10⁻³ Torr or lower beforereactant gase is fed into the vessel at a predetermined flow rate. Thenthe interior of the reactor vessel is maintained at a vacuum of 0.01 to10 Torr. When the flow rate of the reactant gas becomes constant, thevariable frequency power is turned on to generate a plasma with which apolymerized film is formed on the subject.

In the plasma polymerization, a carrier gas may be used such as argon,helium, nitrogen and hydrogen.

The frequency of the power source is not critical to the plasmapolymerization according to the present invention. The source may be ofDC, AC, high frequency and microwave. It is to be noted that otherparameters including supply current and reacting time may be as usual orproperly selected without undue experimentation.

The plasma-polymerized film of organometallic compound is formed in thisway to a thickness of 30 to 300 Å, preferably 50 to 300 Å.Plasma-polymerized films of less than 30 Å are too thin to accomplishthe desired effect whereas films of more than 300 Å are practicallyundesired because of increased spacing losses.

The plasma-polymerized organometallic film preferably contains metalatoms M and carbon atoms C in an atomic ratio M/C of 0.05:1 to 1.0:1,more preferably 0.08:1 to 0.8:1. Atomic ratios M/C of less than 0.05little contribute to adhesion improvement whereas films having atomicratios of more than 1.0:1 are too hard.

The plasma-polymerized film is a three dimensionally grown thin film ofuniform thickness which firmly adheres to the underlying subject (e.g.substrate). Thus the medium having the plasma-polymerized filminterposed therein exhibits very high durability.

The plasma-polymerized organometallic film 7 is generally formeddirectly on the metal thin film magnetic layer 5 as illustrated in FIG.3. On the protective film 7 of plasma-polymerized organometalliccompound is formed a topcoat 9 of plasma-polymerized fluorine or siliconcompound with or without interposing a protective film 8 of carbon. Theplasma-polymerized organometallic film 7 plays a role of an intermediatelayer for joining together the metal thin film magnetic layer 5 and thetopcoat 9 or the protective carbon film 8 when applied. Because of thecombined physical properties of metal and organic matter, theplasma-polymerized organometallic film imparts outstandingly improvedstrength to the bonding interface in the resulting laminate structure.The durability of the resulting medium is markedly improved.

Topcoat

On the plasma-polymerized organometallic film 7 is formed the topcoatlayer 9, particularly plasma-polymerized film containing fluorine orsilicon as described above.

The plasma-polymerized topcoat film may be prepared by substantially thesame plasma polymerizing method as previously described. The presence offluorine or silicon in the film is effective in improving durability,particularly durability as evaluated by a CSS test.

With respect to the plasma-polymerized topcoat film containing fluorine,the material, preparation, fluorine and carbon composition anddistribution, and other parameters involved are the same as previouslydescribed in conjunction with the second embodiment.

Now, the plasma-polymerized topcoat film containing silicon will bedescribed. Silicon may be contained in the plasma-polymerized film bypolymerizing a silicon containing compound with the aid of a plasmaaccording to essentially the same plasma polymerizing procedure aspreviously described.

The reactant gases used herein include, for example, silicon hydride,tetramethylsilane, hexamethyldisilane,1,1,3,3,5,5-hexamethylcyclotrisilazane, tetravinylsilane,3,3,3-trifluoropropyltrichlorosilazane,methyl-3,3,3-trifluoropropyldichlorosilane,3,3,3-trifluoropropyltrimethoxysilane, tetramethoxysilane,tetraethoxysilane, octamethylcyclotetrasiloxane,hexamethylcyclosiloxane, hexamethoxydisiloxane, hexaethoxydisiloxane,triethoxyvinylsilane, dimethylethoxyvinylsilane, trimethoxyvinylsilane,methyltrimethoxysilane, dimethoxymethylchlorosilane,dimethoxymethylsilane, trimethoxysilane, dimethylethoxysilane,trimethoxysilanol, hydroxymethyltrimethylsilane, methoxytrimethylsilane,dimethoxydimethylsilne, ethoxytrimethoxysilane,bis(2-chloroethoxy)methylsilane, acetoxytrimethylsilane,chloromethyldimethylethoxysilane, 2-chloroethoxytrimethylsilane,ethoxytrimethylsilane, diethoxymethylsilane, ethyltrimethoxysilane,tris(2-chloroethoxy)silane, dimethoxymethyl-3,3,3-trifluoropropylsilane,1-chloromethyl-2-chloroethoxytrimethylsilane, allyloxytrimethylsilane,ethoxydimethylvinylsilane, isopropylphenoxvt-rimethylsilane,3-chloropropyldimethoxymethylsilane, chloromethyldiethoxymethylsilane,triethoxychlorosilane, 3-chloropropyltrimethoxysilane,diethoxydimethylsilane, dimethoxy-3-mercaptopropylmethylsilane,triethoxysilane, 3-mercaptopropyltrimethoxysilane,3-aminopropyltrimethoxysilane, diethoxymethylvinylsilane,chloromethyltriethoxysilane, tert.-butoxytrimethylsilane,butyltrimethoxysilane, methyltriethoxysilane,3-(N-methylaminopropyl)triethoxysilane, diethoxydivinylsilane,diethoxydiethylsilane, ethyltriethoxysilane,2-mercaptoethyltriethoxysilane, 3-aminopropyldiethoxydimethylsilane,p-chlorophenyltriethoxysilane, phenyltrimethoxysilane,2-cyanoethyltriethoxysilane, allyltriethoxysilane, triethoxysilane,3-chloropropyltriethoxysilane, 3-allylaminopropyltrimethoxysilane,propyltriethoxysilane, hexatrimethoxysilane,3-aminopropyltriethoxysilane, 3-methylacryloxypropyltrimethoxysilane,methyltris(2-methoxyethoxy)silane, diethoxymethylphenylsilane,p-chlorophenyltriethoxysilane, phenyltriethoxysilane,tetraallyloxysilane, tetrapropoxysilane, tetraisopropoxysilane,dimethoxydiphenylsilane, diethoxydiphenylsilane, tetraphenoxysilane,1,1,3,3-tetramethyldisiloxane, hexamethyldisiloxane,octamethyltrisiloxane, 1,1,1,3,5,5,5-heptamethyltrisiloxane,hexaethylcyclotrisiloxane, and1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane. Also useful arefluorinated silicon compounds such as tetrafluorosilane,hexafluorodisilane, and octafluorotrisilane. A mixture of them may alsobe used.

A mixture of any one or more members of the above-mentioned siliconcompounds and one or more members of fluorinated carbon compounds,fluorinated hydrocarbons, and hydrocarbons may be used.

The silicon-containing topcoat film contains 5 to 50 atom % of carbon.The content of silicon is such that the atom ratio of silicon to carbon(Si/C) ranges from 0.5:1 to 20:1, more preferably from 1:1 to 18:1.Friction reduction is insufficient with Si/C ratios of less than 0.5:1.Polymerized films having Si/C ratios of more than 20:1 are rather weak.Elemental analysis may be carried out by the same procedure aspreviously described.

The plasma-polymerized film topcoat has a thickness of 3 to 300 Åirrespective of whether it contains fluorine or silicon. A thickness inexcess of 300 Å results in an undesirably increased spacing loss. Lessthan 3 Å fails to provide the benefits of the invention.

Preferably, the topcoat layer has a contact angle with water in therange from 60° to 130°, more preferably from 65° to 125°. Topcoat layershaving a contact angle of less than 60° exhibit a higher initialfriction and are unacceptable for actual utility. Plasma-polymerizedfilms having a contact angle of more than 130° are difficult to form andunnecessary for most applications. In the case of thefluorine-containing topcoat, preferably the contact angle ranges from100° to 130°, more preferably from 110° to 125°.

The film thickness may be measured by means of an ellipsometer and canbe controlled by a choice of the reaction time, feed gas flow rate andother factors during film formation by plasma polymerization.

As preferred in the fluorine-containing plasma-polymerized film topcoat,it is also preferred to form the silicon-containing topcoat film suchthat silicon is rich in a surface region of the film. That is, theatomic ratio of silicon to carbon (Si/C) increases toward the surface ofthe film. More illustratively, in the plasma-polymerized topcoat film,the average Si/C atom ratio in the upper region of the film that extendsfrom the surface remote from the substrate to 1/3rd of its thickness isat least 1.5 times, more preferably at least twice that in the lowerregion of the film that extends from the surface adjacent to thesubstrate to 1/3rd of its thickness. Such a graded silicon distributionresults in improved durability.

It is, of course, possible to incorporate both fluorine and silicon inthe topcoat layer according to the present invention.

Preferably, the plasma-polymerized film is prepared by feeding a gaseousreactant into a plasma zone with W/F.M set to at least 10⁷ joule/kgwhere W is an input power applied for plasma generation as expressed injoule/sec., F is a flow rate of the reactant gas as expressed inkg/sec., and M is the molecular weight of the reactant If W/F.M is lessthan 10⁷, the resulting plasma-polymerized film is insufficiently denseto provide the desired corrosion resistance. The upper limit ofparameter W/F M is generally about 10¹⁵ joule/kg.

With respect to the nonmagnetic substrate 2, undercoat layer 3, andintermediate nonmagnetic metal layer 4, the same as previously describedin conjunction with the first embodiment also applies to the thirdembodiment including material, preparation, surface processing and otherparameters.

Further, an additional protective film of nonmagnetic metal may beformed between the metal thin film magnetic layer 5 and the protectivefilm 7 of plasma-polymerized organometallic compound although thisarrangement is not shown in FIG. 3.

The protective carbon layer 8 may preferably formed directly on theprotective film 7 of plasma-polymerized organometallic compound Theprovision of the protective carbon layer further improves durability andweatherability The protective carbon layer generally consists of carbonalone, but may contain up to 5% by weight of another element. It ispreferably formed by sputtering as previously described.

Preferably a plasma treatment is carried out before the protective film7 of plasma-polymerized organometallic compound is formed. Moreparticularly, the surface of the magnetic layer 5 is plasma treated. Inaddition, the protective carbon film 8 is preferably plasma treated atits surface prior to its covering with the topcoat layer. The plasmatreatment chemically activates the surface of the layer so that theoverlying layer may be more firmly bonded to the underlying layer. Thebond strength between the adjoining layers is then increased, offeringsignificantly increased durability The plasma treatment may be carriedout as previously described.

Although the essential layers for each embodiment are described indetail, such essential elements and optional elements are alsoapplicable to different embodiments. For example, provision of aprotective plasma-polymerized film and a protective carbon layer arealso applicable to the second and third embodiments. Any desiredcombination of undercoat, intermediate and protective layers may beadditionally provided in the respective embodiments.

Although the magnetic recording medium is described as a single-siderecording medium as shown in FIGS. 1-3, it may be a double-siderecording medium wherein a series of layers including a magnetic layerare formed on each surface of a substrate in a similar manner as inFIGS. 1-3.

The magnetic recording media according to the present invention exhibitimproved durability, abrasion resistance, weatherability, and corrosionresistance as well as minimized head grip, offering high reliability inactual service.

EXAMPLES

In order that those skilled in the art will better understand thepractice of the present invention, examples of the present inventionwill be described below.

EXAMPLE 1

On a disk-shaped aluminum substrate having a diameter of 13 cm and athickness of 1.9 mm was formed an undercoat layer of NiP to a thicknessof 20 μm by electroless plating. The electroless plating was carried outby successively conducting the following steps under the describedconditions.

NiP Electroless Plating Steps and Their Conditions

(1) Alkaline degreasing: Alprep 204 (Okuno Seiyaku K.K.) 250 ml/l, 65°C., 5 min.

(2) Acidic degreasing: Alprep 230 (Okuno Seiyaku K.K.) 150 ml/l, 65° C.,5 min.

(3) Zincate: Arp 302 (Okuno Seiyaku K.K.) 250 ml/l, 25° C., 30 sec.

(4) Zincate removal: 62 vol % conc. nitric acid 600 ml/l, 25° C., 30sec.

(5) Zincate: Arp 302 (Okuno Seiyaku K.K.) 250 ml/l, 25° C., 20 sec.

(6) Surface adjustment: sodium bicarbonate 30 g/l, 20° C., 30 sec.

(7) Nickel plating: Niclad 719A (Okuno Seiyaku K.K.) 80 ml/l+Niclad 719B(Okuno Seiyaku K.K.) 150 ml/l, pH 4.5, 90° C., 2 hours.

The thus deposited undercoat layer had a composition of Ni:P equal to85:15 in weight ratio and a thickness of 20 μm.

In addition to the aluminum substrate having an undercoat of NiP carriedthereon, substrates of various materials including aluminum, glass(available from Corning Glass), and plastics (polyetherimide resin) werealso employed as reported in Table 1.

Then, the surface of various substrates (or the surface of the undercoatlayer if the substrate has an undercoat on its surface) was abradedunder the following conditions.

Surface Abrasion

The lapping machine used was Model 9B-5P manufactured by Speedfam K.K.While the substrate is being rotated, its surface was abraded using anabrasion liquid, Medipole No. 8 (50% diluted) manufactured by FujimiKenma K.K. under a load of 100 grams for 10 minutes.

The abraded substrate was cleaned in a disk cleaning apparatus availablefrom Speedfam Clean System K.K. This cleaning includes the followingsteps.

Cleaning

(1) Neutral detergent solution, dipping and ultrasonic cleaning,

(2) Superpure water, scrubbing,

(3) Superpure water, scrubbing,

(4) Superpure water, dipping and ultrasonic cleaning,

(5) Superpure water, dipping,

(6) Fron/ethanol mixture, dipping and ultrasonic cleaning,

(7) Fron/ethanol mixture, dipping,

(8) Fron/ethanol mixture, evaporation,

(9) Drying

After the cleaning procedure, the surface of the substrate (or thesurface of the undercoat layer if the substrate has an undercoat on itssurface) was provided with irregularities by a texturizing procedure asdescribed below. Using a tape polishing machine manufactured by TomoeTechno K.K., irregular grooves were formed on the substrate surface in aconcentric pattern while the substrate is being rotated. The polishingparameters are: polishing tape #4000, contact pressure 1.2 kg/cm²,oscillation 50 cycles/min., and 150 work revolutions per minute.

After the substrate was cleaned again by substantially the sameprocedures as described above, the substrate was subjected to an etchingtreatment under an argon gas pressure of 0.2 Pa and an RF power of 400W, and chromium was sputtered to form a nonmagnetic metal intermediatelayer on the substrate to a thickness of 2,000 Å. The sputteringparameters are: argon pressure 2.0 Pa and DC 8 kilowatts.

Thereafter, one of the following variety of metal thin film magneticlayers was formed contiguous to the intermediate layer. It should benoted that in case the magnetic layer be formed by electroless plating,the etching treatment mentioned above and the nonmagnetic metalintermediate layer of Cr were omitted.

Preparation of Metal Thin Film Magnetic Layer Magnetic Layer No. 1 (ML1)

A CoNi magnetic layer was formed by sputtering under an argon pressureof 2.0 Pa and DC 8 kilowatts. The CoNi composition was Co/Ni=80/20 inweight ratio. The film thickness was 600 Å.

Magnetic Layer No. 2 (ML2)

A CoNiCr magnetic layer was formed by sputtering under an argon pressureof 2.0 Pa and DC 8 kilowatts. The CoNiCr composition wasCo/Ni/Cr=62.5/30/7.5 in weight ratio. The film thickness was 600 Å.

Magnetic Layer No. 3 (ML3)

A CoCr magnetic layer was formed by sputtering under an argon pressureof 2.0 Pa and DC 8 kilowatts. The CoCr composition was Co/Cr=87/13 inweight ratio. The film thickness was 1000 Å.

Magnetic Layer No. 4 (ML4)

A CoNiP magnetic layer was formed by electroless plating underconditions described below. The CoNiP composition was Co/Ni/P=6/4/1 inweight ratio. The film thickness was 1000 Å.

The steps and conditions of the electroless plating process are givenbelow.

(1) Alkaline degreasing: Alprep 204 (Okuno Seiyaku K.K.) 250 ml/l, 65°C., 5 min.

(2) Acidic degreasing: Alprep 230 (Okuno Seiyaku K.K.) 150 ml/l, 65° C.,5 min.

(3) Hydrochloric acid degreasing: 5 vol % HCl, 25° C., 1 min.

(4) Sulfuric acid degreasing: 5 vol % H₂ SO₄, 25° C., 1 min.

(5) Nickel plating: Niclad 719A (Okuno Seiyaku K.K.) 80 ml/l+Niclad 719B(Okuno Seiyaku K.K.) 150 ml/l, pH 4.5, 90° C., 30 sec.

    ______________________________________                                        Cobalt sulfate     0.06                                                       Nickel sulfate     0.04                                                       Sodium hypophosphite                                                                             0.25                                                       Rochelle salt      1.00                                                       Ammonium sulfate   0.40                                                       Boric acid         0.10                                                       ______________________________________                                    

plus NaOH, pH 9.5, 70° C., 3 min.

On each of the various metal thin film magnetic layers thus depositedwas formed a protective nonmagnetic metal film of Cr. Film depositionwas by sputtering chromium under an argon gas pressure of 2.0 Pa and DC8 kilowatts. The film was 200 Å thick.

It is to be noted that only when the metal thin film magnetic layer isof magnetic layer No. 4 as identified above, the surface of the metalthin film magnetic layer was etched under an argon gas pressure of 0.2Pa and an RF power of 400 watts immediately before the protectivenonmagnetic metal film was deposited.

The surface of the protective nonmagnetic metal film was subjected to aplasma treatment under the following conditions.

    ______________________________________                                        Plasma Treatment                                                              ______________________________________                                        Treating gas:         Ar                                                      Gas flow rate:        50 ml/min.                                              Vacuum:               0.1 Torr                                                Power frequency:      13.56 MHz                                               Treating time:        30 seconds                                              ______________________________________                                    

On the plasma-treated surface of the protective monmagnetic metal film,each of various plasma-polymerized films as reported in Table 1 wasformed.

More particularly, the coated substrate was placed in a vacuum chamber,which was evacuated to a vacuum of 10⁻³ Torr and then charged withpredetermined flow rates of a selected gaseous hydrocarbon monomer andan argon carrier gas so as to maintain a gas pressure of 0.1 Torr. Ahigh frequency voltage was applied at 13.56 MHz and 10 to 5,000 watts togenerate a plasma flame, with which the hydrocarbon monomer waspolymerized to form a plasma-polymerized film. The thickness of the thusformed film is reported in Table 1.

It is to be noted that elemental analysis of these plasma-polymerizedfilms was made by SIMS and film thickness was measured by means of anellipsometer.

The surface of the plasma-polymerized film was cleaned with unwovenfabric. On top of the plasma-polymerized film was formed a topcoat layerby depositing a topcoat composition containing selected one of variousorganic fluorine compounds as mentioned below using spin coating andvacuum deposition. All the topcoat layers were formed to a thickness of30 Å.

Topcoat Layer Composition Topcoat Composition 1 (TC1)

The topcoat layer was formed by spin coating. The organic fluorinecompound used was KRYTOX 157FS commercially available from E. I. DuPontand having the structural formula: ##STR7## wherein n is 11 to 49. Thefluorine compound was mixed with a solvent, Fron 113 (Daifron S-3available from Daikin Kogyo K.K.) to form a coating solution containing0.05% by weight of the fluorine compound. The solution was spin coatedat 1,000 revolutions per minute for 10 seconds.

Topcoat Composition 2 (TC2)

The topcoat layer was deposited by vacuum deposition. The evaporationsource used was the solids of FOMBLIN Y 25 having a molecular weight of3,000 and commercially available from Montefluos Company. Theevaporation conditions included an argon atmosphere at a pressure of1×10⁻² Pa and a sample-to-source distance of 5 cm.

Topcoat Composition Si-Oil

The material used was a silicone oil (Toshiba Silicone TSF451) having aviscosity of 1,000 centipoise. The material was mixed with a Fron 113solvent to form a coating solution containing 0.05% by weight of thematerial. The solution was spin coated under the same conditions as TC1.

Coating composition Si-Oil, which is outside the scope of the presentinvention, was employed for comparative purposes.

In this way, a number of magnetic disk samples were fabricated asreported in Table 1 and measured for various properties.

It should be noted that in sample No. 13, the plasma-polymerized filmaccording to the present invention was replaced by a sputtered carbonfilm. The sputtered film was 300 Å thick.

(1) Weatherability

A 51/4-inch magnetic disk was loaded in a disk drive and placed in aclean, constant-temperature, constant-humidity chamber where the diskwas allowed to stand for one month at 70° C. and RH 90%. The number oferrors per disk recording side of the disk sample was counted using adisk certifier manufactured by Hitachi Electronic Engineering K.K. withthe slicing level of missing pulses set at 65%. An increase of thenumber of errors or missing pulses before and after the weathering testwas reported in bits per side.

(2) Coefficient of friction (μ)

After a 30,000-cycle contact start-and-stop (CSS) test, the disk incontact with the head was allowed to stand at 20° C. and RH 60% forthree days. The surface of the disk sample was measured for coefficientof friction. The head used was an Mn-Zn ferrite head.

The results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                  Plasma-Polymerized Film                                         Sample   Magnetic   W(F.M.)                                                                             C      Thickness  Weather-                          No. Substrate                                                                          Layer                                                                              Reactant                                                                            (Joule/Kg)                                                                          (at %)                                                                            C/H                                                                              (Å)                                                                             Topcoat                                                                            ability                                                                            μ                         __________________________________________________________________________    101 Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              300   TC1  0    0.25                         102 Al   ML1  C.sub.2 H.sub.2 + N.sub.2                                                           7 × 10.sup.9                                                                  72  3.2                                                                              300   TC1  0    0.27                                                   (N:5)                                               103 Al   ML1  C.sub.2 H.sub.6                                                                     5 × 10.sup.9                                                                  81  4.2                                                                              300   TC1  0    0.24                         104 Al   ML1  CH.sub.4                                                                            6 × 10.sup.5                                                                  17  0.2                                                                              300   TC1  8    0.29                         105 Al   ML1  CH.sub.4                                                                            5 × 10.sup.10                                                                 89  8.5                                                                              300   TC1  3    0.28                         106 Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              300   TC2  0    0.20                         107*                                                                              Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              300   Si--Oil                                                                            25   0.98                         108 Al   ML2  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              500   TC1  0    0.26                         109 Al   ML3  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              800   TC1  0    0.27                         110 Al   ML4  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              300   TC1  0    0.27                         111*                                                                              Al   ML1  --    --    --  -- --    TC1  >1000                                                                              >1.0                         112*                                                                              Al   ML1  --    --    --  -- --    --   >1000                                                                              >1.0                         113*                                                                              Al   ML1  --    --    --  -- --    TC1  16   0.35                         114 Glass                                                                              ML2  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              300   TC1  0    0.28                         115 Plastics                                                                           ML2  CH.sub.4                                                                            5 × 10.sup.8                                                                  67  2.0                                                                              300   TC1  2    0.29                         __________________________________________________________________________     *comparison                                                              

EXAMPLE 2

The procedure of Example 1 was repeated until the plasma-polymerizedfilm was formed on the magnetic layer except that the protectivechromium film was 50 Å thick and the plasma treatment on the protectivechromium film used hydrogen instead of argon. In this example, theplasma-polymerized film formed on the magnetic layer in the same manneras in Example 1 is referred to as a first plasma-polymerized film.

On the first plasma-polymerized film, a protective carbon film wasformed by sputtering carbon under an argon gas pressure of 0.2 Pa and DC8 kilowatts. The protective film was 250 Å thick.

The surface of the protective carbon film was plasma treated under thesame conditions as used in the plasma treatment of the surface of theprotective nonmagnetic metal film.

A second plasma-polymerized film was formed on the protective carbonfilm as desired. More particularly, in sample Nos. 201 to 210, 213, and214, the second plasma-polymerized film was formed on the protectivecarbon film under the same conditions as used in the formation of thecorresponding first plasma-polymerized film. That is, in these samples,the first and second plasma-polymerized films were identical. In sampleNos. 217 and 218, second plasma-polymerized films which were the same asthe first plasma-polymerized films of sample Nos. 201 and 202 wereformed on the protective carbon film, respectively.

The surface of the plasma-polymerized film was cleaned with unwovenfabric. On top of the plasma-polymerized film was formed a topcoat layerby depositing a topcoat composition containing selected one of variousorganic fluorine compounds as mentioned below using spin coating andsputtering. All the topcoat layers were formed to a thickness of 40 Å.

Topcoat Layer Composition Topcoat Composition 1 (TC1)

Same as in Example 1.

Topcoat Composition 22 (TC22)

The topcoat layer was deposited by sputtering. The source material usedas the target in sputtering was KRYTOX 157FS. The resin composition wasapplied onto a plate followed by evaporation of the solvent therefrom,obtaining a plate-like target of the solid resin.

The sputtering conditions included a sputtering power of 3 kW, anoperating pressure of 1 Pa and a sample-to-target distance of 10 cm. Theresin target had dimensions of about 15 cm by 30 cm. The inert gas usedin the sputtering was argon.

Topcoat Composition Si-Oil

Same as in Example 1.

In this way, a number of magnetic disk samples were fabricated asreported in Table 2 and measured for various properties.

(1) CSS

A contact-start-and-stop (CSS) test was carried out. The number oferrors per disk recording side of a magnetic disk sample was countedboth immediately after fabrication and after 30,000contact-start-and-stop cycles. An increase of the number of errors ormissing pulses before and after the CSS test was reported in bits perside.

The number of errors per disk recording side was counted using a diskcertifier manufactured by Hitachi Electronic Engineering K.K. with theslicing level of missing pulses set at 65%.

(2) ΔBm

Using a vibratory specimen type magnetometer, Model VSM-5S manufacturedby Toei Kogyo K.K., the saturated magnetic flux density Bm of a specimencut to a size of 8 mm×8 mm was measured under the maximum appliedmagnetic filed of 15 kilogauss. Measumrent was made both before andafter the specimen was allowed to stand at 60° C. and RH 90% for onemonth. A change ΔBm in the saturated magnetic flux was calculated andexpressed in %. That is, ΔBm=[(Bm after 1-month storage @60° C.,RH90%)-(Bm as fabricated)]/(Bm as fabricated)×100%.

(3) Coefficient of friction (μ)

After a 30,000-cycle contact start-and-stop (CSS) test, the disk incontact with the head was allowed to stand at 20° C. and RH 60% for 24hours. The surface of the disk sample was measured for coefficient offriction. The head used was an Mn-Zn ferrite head.

The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                  1st Plasma-Polymerized Film                                                                       Thick-                                                                            2nd Plasma                              Sample   Magnetic   W/(F.M.)                                                                            C       ness                                                                              Polymerized     ΔBm               No. Substrate                                                                          Layer                                                                              Reactant                                                                            (Joule/Kg)                                                                          (at %)                                                                             C/H                                                                              (Å)                                                                           Film   Topcoat                                                                            CSS (%) μ                __________________________________________________________________________    201 Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 Yes    TC1  0   1.0 0.23                202 Al   ML1  C.sub.2 H.sub.2 + N.sub.2                                                           7 × 10.sup.9                                                                  72 (N:5)                                                                           3.2                                                                              100 Yes    TC1  0   1.2 0.21                203 Al   ML1  C.sub.2 H.sub.6                                                                     5 × 10.sup.9                                                                  81   4.2                                                                              100 Yes    TC1  0   1.4 0.24                204 Al   ML1  CH.sub.4                                                                            6 × 10.sup.5                                                                  17   0.2                                                                              100 Yes    TC1  7   3.1 0.34                205 Al   ML1  CH.sub.4                                                                            5 × 10.sup.10                                                                 89   8.5                                                                              100 Yes    TC1  4   2.3 0.30                206 Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 Yes    TC22 0   1.4 0.23                207*                                                                              Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 Yes    Si--Oil                                                                            22  1.4 0.42                208 Al   ML2  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              150 Yes    TC1  0   1.5 0.22                209 Al   ML3  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              200 Yes    TC1  0   1.4 0.24                210 Al   ML4  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 Yes    TC1  0   1.8 0.25                211*                                                                              Al   ML1  --    --    --   -- --  No     TC1  55  7.5 0.55                212*                                                                              Al   ML1  --    --    --   -- --  No     --   700 8.2 >1.0                213 Glass                                                                              ML2  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 Yes    TC1  0   1.1 0.23                214 Plastics                                                                           ML2  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 Yes    TC22 1   1.2 0.28                215 Al   ML1  CH.sub.4                                                                            5 × 10.sup.8                                                                  67   2.0                                                                              100 No     TC1  0   1.2 0.22                216 Al   ML1  C.sub.2 H.sub.6                                                                     5 × 10.sup.9                                                                  81   4.2                                                                              100 No     TC1  0   1.7 0.23                217 Al   ML1  --    --    --   -- --  Yes    TC1  0   1.5 0.21                218 Al   ML1  --    --    --   -- --  Yes    TC1  0   1.6 0.24                __________________________________________________________________________     *comparison                                                              

EXAMPLE 3

Sample Nos. 101 and 102 of Example 1 and sample Nos. 201 and 202 ofExample 2 were subjected to a durability test as defined below.

Durability Test

A 51/4-inch magnetic disk was loaded in a disk drive which was placed ina constant-temperature chamber at 0° C. The number of errors or missingpulses was counted in bits per side both before and after a 30,000 cycleCSS test. The number of errors per disk recording side of the disksample was counted using a disk certifier manufactured by HitachiElectronic Engineering K.K. with the slicing level of missing pulses setat 65%. An increase of the number of errors or missing pulses before andafter the test was reported in Table 3.

Additional sample Nos. 121, 122, and 123 were fabricated by replacingthe plasma-polymerized film of sample Nos. 101 and 102 by the filmsshown in Table 3. Additional sample Nos. 221, 222, and 223 werefabricated by replacing the plasma-polymerized film of sample Nos. 201and 202 by the films shown in Table 3. They were also tested.

                  TABLE 3                                                         ______________________________________                                        Plasma-polymerized film                                                       Sample Reactant                                                                         W/F.M    C           N    O    Durability                           No.  Reactant joule/kg at % C/H  at % at % bits/side                          ______________________________________                                        101  CH.sub.4 5 × 10.sup.8                                                                     67   2.0  --   --   11                                 102  C.sub.2 H.sub.2 +                                                                      7 × 10.sup.9                                                                     72   3.2  5    --   4                                       N.sub.2                                                                  121  CH.sub.4 +                                                                             5 × 10.sup.8                                                                     52   1.6  16   --   0                                       NH.sub.3                                                                 122  CH.sub.4 +                                                                             5 × 10.sup.8                                                                     47   1.7  20   5    0                                       N.sub.2 O                                                                123  C.sub.2 H.sub.2 +                                                                      5 × 10.sup.8                                                                     55   1.8  --   15   0                                       CO.sub.2                                                                 201  CH.sub.4 5 × 10.sup.8                                                                     67   2.0  --   --   9                                  202  C.sub.2 H.sub.2 +                                                                      7 × 10.sup.9                                                                     72   3.2  5    --   3                                       N.sub.2                                                                  221  CH.sub.4 +                                                                             5 × 10.sup.8                                                                     52   1.6  16   --   0                                       NH.sub.3                                                                 222  CH.sub.4 +                                                                             5 × 10.sup.8                                                                     35   1.7  28   16   0                                       N.sub.2 O                                                                223  C.sub.2 H.sub.2 +                                                                      5 × 10.sup.8                                                                     48   1.8  --   25   0                                       CO.sub.2                                                                 ______________________________________                                    

EXAMPLE 4

The procedure of Example 1 was repeated until the protective nonmagneticmetal film of chromium was formed on the magnetic layer. The thicknessof the protective nonmagnetic metal film was 100 Å.

On the protective film, a protective carbon film was formed to athickness of 300 Å by sputtering carbon under an argon pressure of 0.2Pa with a power of DC 8 kilowatts

The surface of the protective carbon film was plasma treated. Where theprotective carbon film was omitted, the surface of the protectivenonmagnetic metal film was plasma treated.

The plasma treatment was carried out using a treating gas of nitrogenunder a pressure of 5 Pa and applying a power of 3 kilowatts at afrequency of 13.56 MHz.

A topcoat in the form of a plasma-polymerized film was formed on theplasma-treated surface by the following procedure.

The coated substrate was placed in a vacuum chamber, which was evacuatedto a vacuum of 10⁻³ Torr and then charged with a predetermined flow rateof a gaseous reactant as reported in Table 4 so as to maintain a gaspressure of 0.05 Torr. A high frequency voltage was applied at 13.56 MHzto generate a plasma flame, with which the reactant was polymerized toform a plasma-polymerized film. Various parameters of theplasma-polymerized film is reported in Table 4. The heading(F/C)t/(F/C)b in Table 4 is the ratio of the average atom ratio offluorine to carbon (F/C)t in the top region of the topcoat film whichextends from its exposed surface to a depth of 1/3rd of its thickness tothe average atom ratio of fluorine to carbon (F/C)b in the bottom regionof the topcoat film which extends from its surface adjacent to thesubstrate to a level of 1/3rd of its thickness.

The samples were measured for the following properties.

(1) Coefficient of friction (μ)

After a 20,000-cycle contact start-and-stop (CSS) test, the disk incontact with the head was allowed to stand at 20° C. and RH 60% forthree days. The surface of the disk sample was measured for coefficientof friction. The head used was an Mn-Zn ferrite head.

(2) Grip

A Mn-Zn ferrite head was held on the surface of a stationary magneticdisk sample at 20° C. and RH 70% for 48 hours before the sample wassuddenly rotated to measure an initial coefficient of friciton.

(3) Surface observation

At the end of the CSS test, the surface of a sample was observed under ascanning electronmicroscope.

The crazing or cracking state of the surface was evaluated in fourgrades.

E: No crazing

Good: Crazing only on topcoat surface

Fair: Cracks to protective film surface

Poor: Deep cracks to protective and magnetic films

The results are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                  Plasma-Polymerized Topcoat Film              Sur-               Sam-                                        Con-                                                                              Thick-     face               ple                                                                              Sub-                                                                             Magnetic                                                                           C.        W/(F.M.)                                                                            C            (F/C)t                                                                            tact                                                                              ness       Ob-                No.                                                                              strate                                                                           Layer                                                                              Film                                                                             Reactant                                                                             (Joule/Kg)                                                                          (at %)                                                                            F/C                                                                              C/H                                                                              H/F                                                                              (F/C)b                                                                            Angle                                                                             (Å)                                                                           μ                                                                              Grip                                                                             served             __________________________________________________________________________    301                                                                              Al ML1  Yes                                                                              CH.sub.4 + C.sub.3 F.sub.6                                                           2 × 10.sup.10                                                                 47  0.8 4.1                                                                             0.30                                                                             2.1 118 80  0.24                                                                              0.13                                                                             E                  302                                                                              Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.2 122 80  0.23                                                                              0.10                                                                             E                  303                                                                              Al 1    Yes                                                                              C.sub.2 H.sub.6 + C.sub.2 F.sub.4                                                    2 × 10.sup.10                                                                 44  1.0 3.5                                                                             0.29                                                                             2.3 120 80  0.24                                                                              0.11                                                                             E                  304                                                                              Al 1    Yes                                                                              C.sub.2 H.sub.6 + C.sub.2 F.sub.4                                                    5 × 10.sup.8                                                                  43  1.0 2.9                                                                             0.34                                                                             2.1 122 80  0.22                                                                              0.12                                                                             E                  305*                                                                             Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 8 × 10.sup.7                                                                  22  0.2 0.3                                                                             16.7                                                                             2.0 92  80  0.75                                                                              0.28                                                                             Fair               306*                                                                             Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 4 × 10.sup.5                                                                  22  3.2 2.5                                                                             0.13                                                                             2.0 124 80  0.52                                                                              0.23                                                                             Fair               307*                                                                             Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 5 × 10.sup.15                                                                 89  0.1 41.7                                                                            0.24                                                                             2.0 89  80  0.66                                                                              0.25                                                                             Fair               308                                                                              Al ML2  Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.0 122 80  0.21                                                                              0.12                                                                             E                  309                                                                              Al ML3  Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.0 122 80  0.22                                                                              0.11                                                                             E                  310                                                                              Al ML4  Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.0 122 80  0.26                                                                              0.13                                                                             E                  311*                                                                             Al ML1  Yes                                                                              --     --    --  --  --                                                                              -- --  --  --  >1  0.41                                                                             Poor               312*                                                                             Al 1    No --     --    --  --  --                                                                              -- --  --  --  >1  0.62                                                                             Poor               313                                                                              Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             0.5 110 80  0.32                                                                              0.21                                                                             Fair               314                                                                              Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             1.0 121 80  0.29                                                                              0.18                                                                             Good               315                                                                              Al 1    Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             1.5 122 80  0.26                                                                              0.15                                                                             E                  316                                                                              Al 1    Yes                                                                              C.sub.3 F.sub.6                                                                      7 × 10.sup.8                                                                  48  1.1 --                                                                              -- 2.0 122 80  0.23                                                                              0.10                                                                             E                  317                                                                              Glass                                                                            ML2  Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.2 122 80  0.22                                                                              0.10                                                                             E                  318                                                                              Plas-                                                                            ML3  Yes                                                                              CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.2 122 80  0.29                                                                              0.14                                                                             Good                  tics                                                                       319                                                                              Al ML1  No CH.sub.4 + CHF.sub.3                                                                 3 × 10.sup.8                                                                  43  1.0 3.1                                                                             0.32                                                                             2.2 122 400 0.24                                                                              0.11                                                                             E                  320                                                                              Al ML1  No C.sub.2 H.sub.6 + C.sub.2 F.sub.4                                                    2 × 10.sup.10                                                                 49  0.8 4.1                                                                             0.30                                                                             2.1 118 400 0.22                                                                              0.12                                                                             E                  __________________________________________________________________________     *comparison                                                              

EXAMPLE 5

The procedures of Example 1 were followed until the intermediatenonmagnetic metal layer of Cr was formed by sputtering. Thereafter, oneof the following variety of metal thin film magnetic layers was formedcontiguous to the intermediate layer. It should be noted that in casethe magnetic layer be formed by electroless plating, the etchingtreatment of the undercoat and formation of the nonmagnetic metal (Cr)intermediate layer were omitted.

Preparation of Metal Thin Film Magnetic Layer Magnetic Layer No. 51(ML51)

A CoNi magnetic layer was formed by sputtering under an argon pressureof 2.0 Pa and DC 8 kilowatts. The CoNi composition was Co/Ni=80/20 inweight ratio. The film thickness was 600 Å.

The surface of the magnetic layer was then oxidized with a plasma underthe following conditions.

Treating gas: NO₂

Gas flow rate: 10 SCCM (standard cubic centimeter)

Vacuum: 0.05 Torr

Power: 13.56 MHz

The oxidized magnetic layer had the following oxygen to cobalt ratios.

Average O/Co=0.1:1

(O/Co)u=0.8:1

(O/Co)l=0.01:1

It is to be noted that (O/Co)u is the ratio of O/Co in the upper regionof the magnetic layer that extends from its upper or exposed surface toa depth of 1/10th of its thickness. (O/Co)l is the ratio of O/Co in theremaining lower region of the magnetic layer that extends from its lowersurface adjacent to the substrate to a level of 1/10th of its thickness.

Magnetic Layer No. 52 (ML52)

A CoNiCr magnetic layer was formed by sputtering under an argon pressureof 2.0 Pa and DC 8 kilowatts. The CoNiCr composition wasCo/Ni/Cr=62.5/30/7.5 in weight ratio. The film thickness was 600 Å.

The surface of the magnetic layer was then oxidized with a plasma underthe following conditions.

Treating gas: O₂

Gas flow rate: 25 SCCM

Vacuum: 0.01 Torr

Power: 2.45 GHz

The oxidized magnetic layer had the following oxygen to cobalt ratios.

Average O/Co=0.08:1

(O/Co)u=0.5:1

(O/Co)l=0.01:1

Magnetic Layer No. 53 (ML53)

A CoCr magnetic layer was formed by sputtering under an argon pressureof 2.0 Pa and DC 8 kilowatts. The CoCr composition was Co/Cr=87/13 inweight ratio. The film thickness was 1000 Å.

The surface of the magnetic layer was then oxidized with a plasma underthe following conditions.

Treating gas: O₂

Gas flow rate: 25 SCCM

Vacuum: 0.01 Torr

Power: 2.45 GHz

The oxidized magnetic layer had the following oxygen to cobalt ratios.

Average O/Co=0.15:1

(O/Co)u=1.0:1

(O/Co)l=0.008:1

Magnetic Layer No. 54 (ML54)

A CoNiP magnetic layer was formed by electroless plating underconditions described below. The CoNiP composition was Co/Ni/P=6/4/1 inweight ratio. The film thickness was 1000 Å.

The steps and conditions of the electroless plating process are givenbelow.

(1) Alkaline degreasing: Alprep 204 (Okuno Seiyaku K.K.) 250 ml/l, 65°C., 5 min.

(2) Acidic degreasing: Alprep 230 (Okuno Seiyaku K.K.) 150 ml/l, 65° C.,5 min.

(3) Hydrochloric acid degreasing: 5 vol % HCl, 25° C., 1 min.

(4) Sulfuric acid degreasing: 5 vol % H₂ SO₄, 25° C., 1 min.

(5) Nickel plating: Niclad 719A (Okuno Seiyaku K.K.) 80 ml/l+Niclad 719B(Okuno Seiyaku K.K.) 150 l ml/l, pH 4.5, 90° C., 30 sec.

    ______________________________________                                        (6) Cobalt plating: plating bath                                                                   mol/liter                                                ______________________________________                                        Cobalt sulfate       0.06                                                     Nickel sulfate       0.04                                                     Sodium hypophosphite 0.25                                                     Rochelle salt        1.00                                                     Ammonium sulfate     0.40                                                     Boric acid           0.10                                                     ______________________________________                                    

plus NaOH, pH 9.5, 70° C., 3 min.

The surface of the magnetic layer was then oxidized with a plasma underthe following conditions.

Treating gas: O₂

Gas flow rate: 25 SCCM

Vacuum: 0.01 Torr

Power: 2.45 GHz

The oxidized magnetic layer had the following oxygen to cobalt ratios.

Average O/Co=0.20:1

(O/Co)u=0.1:1

(O/Co)l=0.02:1

Magnetic Layer No. 55 (ML55)

It was the same as magnetic layer No. 51 except that the plasmaoxidation was omitted.

Magnetic Layer No. 56 (ML56)

It was the same as magnetic layer No. 52 except that the plasmaoxidation was omitted.

Magnetic Layer No. 57 (ML57)

It was the same as magnetic layer No. 53 except that the plasmaoxidation was omitted.

Magnetic Layer No. 58 (ML58)

It was the same as magnetic layer No. 54 except that the plasmaoxidation was omitted.

Magnetic layer Nos. 55-58 had average O/Co ratios between 0.005:1 and0.05:1.

On each of the various metal thin film magnetic layers thus depositedwas formed a protective nonmagnetic metal film of Cr. Film depositionwas by sputtering chromium under an argon gas pressure of 2.0 Pa and DC8 kilowatts. The film was 100 Å thick.

It is to be noted that only when the metal thin film magnetic layers areof magnetic layers Nos. 54 and 58 as identified above, the surfaces ofthe metal thin film magnetic layers were etched under an argon gaspressure of 0.2 Pa and an RF power of 400 watts immediately before theprotective nonmagnetic metal film was deposited.

On the protective nonmagnetic metal film was formed a topcoat in theform of a plasma-polymerized film. The coated substrate was placed in avacuum chamber, which was evacuated to a vacuum of 10⁻³ Torr and thencharged with a predetermined flow rate of a gaseous reactant as reportedin Table 5 so as to maintain a gas pressure of 0.05 Torr. A highfrequency voltage was applied at 13.56 MHz to generate a plasma flame,with which the reactant was polymerized to form a plasma-polymerizedfilm. Various parameters of the plasma-polymerized film is reported inTable 5. The heading (F/C)t/(F/C)b in Table 5 is the ratio of theaverage atom ratio of fluorine to carbon (F/C)t in the top region of thetopcoat film which extends from its exposed surface to a depth of 1/3rdof its thickness to the average atom ratio of fluorine to carbon (F/C)bin the bottom region of the topcoat film which extends from its surfaceadjacent to the substrate to a level of 1/3rd of its thickness.

Sample No. 415 had a protective carbon a film of 100 Å thick formed onthe protective nonmagnetic metal film. The topcoat was formed on thecarbon film.

In sample No. 417, the surface of the protective nonmagnetic metal filmwas plasma treated before the topcoat was formed. The plasma treatingconditions were treating gas N₂, pressure 5 Pa, source 13.56 MHz highfrequency, and power supplied 3 kilowatts.

In this way, a number of magnetic disk samples were fabricated asreported in Table 5 and measured for (1) CSS characteristics and (2)coefficient of friction (μ) both by the same methods as described inExample 2.

The results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                  Plasma-polymerized topcoat film                                 Sample   Magnetic     W/F.M Thickness                                                                           C          (F/C)t                                                                            Contact                                                                           CSS error                No. Substrate                                                                          Layer                                                                              Reactant                                                                              (Joule/Kg)                                                                          (Å)                                                                             (at %)                                                                            F/C                                                                              H/F (F/C)b                                                                            angle                                                                             (bits/side)                                                                         μ               __________________________________________________________________________    401 Al   ML51 CF.sub.4 + C.sub.3 F.sub.6                                                            2 × 10.sup.10                                                                 300   49  0.8                                                                             0.30 2.0 118 0     0.18               402*                                                                              Al   ML55 CF.sub.4 + C.sub.3 F.sub.6                                                            2 × 10.sup.10                                                                 300   49  0.8                                                                             0.30 2.0 118 11    0.24               403 Al   ML52 CH.sub.4 + CHF.sub.3                                                                  3 × 10.sup.9                                                                  300   43  1.0                                                                             0.35 2.2 120 0     0.17               404*                                                                              Al   ML56 CH.sub.4 + CHF.sub.3                                                                  3 × 10.sup.9                                                                  300   43  1.0                                                                             0.35 2.2 120 10    0.23               405 Al   ML53 C.sub.2 H.sub.6 + C.sub.2 F.sub.4                                                     5 × 10.sup.10                                                                 300   37  1.2                                                                             0.45 2.0 121 0     0.19               406*                                                                              Al   ML57 C.sub.2 H.sub.6 +  C.sub.2 F.sub.4                                                    5 × 10.sup.10                                                                 300   37  1.2                                                                             0.45 2.0 121 12    0.25               407 Al   ML54 CH.sub.4 + C.sub.2 F.sub.4                                                            7 × 10.sup.8                                                                  300   35  1.4                                                                             0.32 2.1 122 0     0.17               408*                                                                              Al   ML58 CH.sub.4 + C.sub.2 F.sub.4                                                            7 × 10.sup.8                                                                  300   35  1.4                                                                             0.32 2.1 122 14    0.26               409 Al   ML51 CH.sub.4 + C.sub.2 F.sub.4                                                            7 × 10.sup.7                                                                  300   87  0.1                                                                             0.51 1.0 91  2     0.31               410 Al   ML51 CH.sub.4 + C.sub.2 F.sub.4                                                            3 × 10.sup.4                                                                  300   22  3.2                                                                             0.13 1.5 124 2     0.30               411*                                                                              Al   ML51 --      --    --    --  --                                                                              --   --  124 60    0.81               412*                                                                              Al   ML55 --      --    --    --  --                                                                              --   --  124 800   >1.0               413 Al   ML51 C.sub.3 F.sub.6                                                                       6 × 10.sup.8                                                                  300   40  1.5                                                                             --   2.0 120 0     0.16               414 Glass                                                                              ML52 CH.sub.4 + CHF.sub.3                                                                  3 × 10.sup.9                                                                  300   43  1.0                                                                             0.35 2.1 120 0     0.18               415 Al   ML51 CH.sub.4 +C.sub.3 F.sub.6                                                             2 × 10.sup.10                                                                 200   49  0.8                                                                             0.30 2.0 118 0     0.15               416 Al   ML51 CH.sub.4 + C.sub.3 F.sub.6                                                            2 × 10.sup.10                                                                 200   49  0.8                                                                             0.30 1.0 115 0     0.21               417 Al   ML51 CH.sub.4 + C.sub.3 F.sub.6                                                            2 × 10.sup.10                                                                 200   49  0.8                                                                             0.30 2.0 118 0     0.15               __________________________________________________________________________     *comparison                                                              

EXAMPLE 6

The procedure of Example 1 was repeated until the metal thin filmmagnetic layer was formed. On each of the various metal thin filmmagnetic layers deposited by the same procedures as in Example 1 wasformed a plasma-polymerized organometallic film under the plasmapolymerization conditions shown below.

Plasma-Polymerized Organometallic Film 1 (PPOM1)

Gaseous monomer: tetramethyltin

Monomer flow rate: 10 ml/min.

Carrier gas: argon

Carrier flow rate: 50 ml/min.

Vacuum: 0.5 Torr

High frequency power source: 13.56 MHz, 200 watts

The polymerized film was measured to have a uniform thickness of 250 Åusing the multiple interference technique and an ellipsometer. Fouriertransformation infrared spectroscopy and electron spectroscopy forchemical analysis (ESCA) showed that the film is a thin polymerized filmcontaining tin. Metal to carbon ratio (M/C)=0.35.

Plasma-Polymerized Organometallic Film 2 (PPOM2)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was titaniumacetylacetonate. The film was 210 Å thick and had a M/C ratio of 0.21:1.

Plasma-Polymerized Organometallic Film 3 (PPOM3)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was dimethylmagnesium.The film was 250 Å thick and had a M/C ratio of 0.31:1.

Plasma-Polymerized Organometallic Film 4 (PPOM4)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was phenylcopper. Thefilm was 280 Å thick and had a M/C ratio of 0.19:1.

Plasma-Polymerized Organometallic Film 5 (PPOM5)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was dimethylzinc. Thefilm was 200 Å thick and had a M/C ratio of 1.1:1.

Plasma-Polymerized Organometallic Film 6 (PPOM6)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was trimethylaluminum.The film was 250 Å thick and had a M/C ratio of 0.10:1.

Plasma-Polymerized Organometallic Film 7 (PPOM7)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was tetraethyltin. Thefilm was 300 Å thick and had a M/C ratio of 0.21:1.

Plasma-Polymerized Organometallic Film 8 (PPOM8)

A polymerized film was deposited under the same conditions as used forpolymerized film 1 except that the monomer used was phenylsilver. Thefilm was 250 Å thick and had a M/C ratio of 0.04:1.

Plasma-Polymerized Organometallic Film 9 (PPOM9)

For comparison purpose, a polymerized film was deposited under the sameconditions as used for polymerized film 1 except that the monomer usedwas ethylene C₂ H₄. The film was 300 Å thick.

A plasma-polymerized topcoat film was formed on the plasma-polymerizedorganometallic film. More particularly, the coated substrate was placedin a vacuum chamber, which was evacuated to a vacuum of 10⁻³ Torr andthen charged with a predetermined flow rate of a selected gaseousreactant so as to maintain a gas pressure of 0.05 Torr. A high frequencyvoltage was applied at 13.56 MHz to generate a plasma flame, with whichthe reactant was polymerized to form a plasma-polymerized film. Thethickness of the thus formed film is reported in Table 6. The heading xin Table 6 is the ratio of the average atom ratio of fluorine or siliconto carbon (F or Si/C)t in the top region of the topcoat film whichextends from its exposed surface to a depth of 1/3rd of its thickness tothe average atom ratio of fluorine or silicon to carbon (F or Si/C)b inthe bottom region of the topcoat film which extends from its surfaceadjacent to the substrate to a level of 1/3rd of its thickness, that is,(F/C)t/(F/C)b or (Si/C)t/(Si/C)b.

In this way, a number of magnetic disk samples were fabricated asreported in Table 6 and measured for various properties.

For sample No. 522, a protective carbon film was formed on theplasma-polymerized organometallic film by sputtering to a thickness of100 Å. For sample No. 523, the surface of the magnetic layer was plasmatreated before the formation of plasma-polymerized organometallic film.The plasma treating conditions were treating gas N₂, pressure 5 Pa,source 13.56 MHz high frequency, and power supplied 3 kilowatts.

(1) CSS ed out.

A contact-start-and-stop (CSS) test was carried out. The number oferrors per disk recording side of a magnetic disk sample was countedboth immediately after fabrication and after 40,000contact-start-and-stop cycles. An increase of the number of errors ormissing pulses before and after the CSS test was reported in bits perside.

The number of errors per disk recording side was counted using a diskcertifier manufactured by Hitachi Electronic Engineering K.K. with theslicing level of missing pulses set at 60%.

(2) Coefficient of friction (μ)

After the 40,000-cycle CSS test, the disk in contact with the head wasallowed to stand at 20° C. and RH 60% for three days. The surface of thedisk sample was measured for coefficient of friction. The head used wasan Mn-Zn ferrite head.

(3) Surface observation

At the end of the CSS test, the surface of a sample was observed under ascanning electronmicroscope.

The crazing or cracking state of the surface was evaluated in fourgrades.

E: No crazing

Good: Crazing only on topcoat surface

Fair: Cracks to protective film surface

Poor: Deep cracks to protective and magnetic films

The results are shown in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                       Plasma-polymerized topcoat film                            Sample   Magnetic                                                                           PPOM         Thickness                                                                           C            CSS error  Surface              No. Substrate                                                                          Layer                                                                              Film Reactant                                                                              (Å)                                                                             (at %)                                                                            F/C                                                                              Si/C                                                                             x  (bits/side)                                                                          μ                                                                              observed             __________________________________________________________________________    501 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.21                                                                              E                    502 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   43  1.3                                                                              -- 1.0                                                                              1      0.27                                                                              E                    503 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            2     45  1.2                                                                              -- 1.0                                                                              5      0.48                                                                              Good                 504 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            450   45  1.2                                                                              -- 1.0                                                                              0      0.68                                                                              E                    505*                                                                              Al   ML1  PPOM1                                                                              C.sub.3 H.sub.8                                                                       150   68  -- -- -- 12     0.55                                                                              Poor                 506 Al   ML1  PPOM2                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.20                                                                              E                    507 Al   ML1  PPOM3                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.22                                                                              E                    508 Al   ML1  PPOM4                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.23                                                                              E                    509 Al   ML1  PPOM5                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              2      0.26                                                                              Good                 510*                                                                              Al   ML1  PPOM9                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              15     0.85                                                                              Poor                 511*                                                                              Al   ML1  --   CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              52     >1.0                                                                              Poor                 512 Al   ML1  PPOM1                                                                              CH.sub.4 +                                                                            150   31  -- 2.2                                                                              2.0                                                                              0      0.19                                                                              E                                       Tetramethoxy-                                                                 silane                                                     513 Al   ML1  PPOM6                                                                              CH.sub.4 +                                                                            150   34  -- 2.2                                                                              2.1                                                                              0      0.23                                                                              E                                       Tetramethoxy-                                                                 silane                                                     514 Al   ML1  PPOM7                                                                              CH.sub.4 +                                                                            150   33  -- 2.2                                                                              2.2                                                                              0      0.21                                                                              E                                       Tetramethoxy-                                                                 silane                                                     515 Al   ML1  PPOM8                                                                              CH.sub.4 +                                                                            150   31  -- 2.2                                                                              1.0                                                                              3      0.28                                                                              Good                                    Tetramethoxy-                                                                 silane                                                     516*                                                                              Al   ML1  PPOM9                                                                              CH.sub.4 +                                                                            150   31  -- 2.2                                                                              1.0                                                                              18     0.81                                                                              Poor                                    Tetramethoxy-                                                                 silane                                                     517*                                                                              Al   ML1  --   --      --    --  -- -- -- >100   >1.0                                                                              Poor                 518 Al   ML2  PPOM1                                                                              C.sub.2 F.sub.6                                                                       150   43  1.3                                                                              -- 2.0                                                                              0      0.23                                                                              E                    519 Al   ML3  PPOM1                                                                              C.sub.2 F.sub.6                                                                       150   43  1.3                                                                              -- 2.0                                                                              0      0.20                                                                              E                    520 Al   ML4  PPOM1                                                                              C.sub.2 F.sub.6                                                                       150   43  1.3                                                                              -- 2.0                                                                              1      0.22                                                                              E                    521 Glass                                                                              ML2  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.19                                                                              E                    522 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.18                                                                              E                    523 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   45  1.2                                                                              -- 2.0                                                                              0      0.18                                                                              E                    524 Al   ML1  PPOM1                                                                              CH.sub.4 + C.sub.2 F.sub.4                                                            150   25  2.2                                                                              -- 1.0                                                                              3      0.30                                                                              Good                 525 Al   ML1  PPOM1                                                                              CH.sub.4 + SiH.sub.4                                                                  150   60  -- 0.2                                                                              1.0                                                                              3      0.31                                                                              Good                 __________________________________________________________________________     *comparison                                                              

The data in Tables demonstrate the effectiveness of the presentinvention.

The foregoing description has been made in conjunction with somepreferred embodiments of the present invention. Modifications andchanges may be made on the preferred embodiments without departing fromthe scope of the present invention.

We claim:
 1. A magnetic recording medium comprising a nonmagnetic rigidsubstrate having opposed major surfaces,a metal thin film magnetic layerdisposed on one major surface of the substrate, and a topcoat layer onthe magnetic layer, said topcoat layer comprising a plasma-polymerizedfilm containing carbon, fluorine, wherein the carbon content ranges from30 to 80 atom %, the hydrogen-to fluorine atom ratio ranges from 0.1.0to 1.0:1.0, and the average fluorine-to-carbon atom ratio (F/C) in theregion of said film that extends from the surface remote from thesubstrate to 1/3rd of its thickness is at least 1.5 times that in theregion of the film that extends from the surface adjacent to thesubstrate to 1/3rd of its thickness, said plasma-polymerized film beingprepared by activating a gaseous reactant into a plasma to generateactive species thereof while feeding the reactant into a plasma zonewith W/F.M set to 10⁷ to 10¹⁵ joule/kg, wherein W is an input powerapplied for plasma generation, F is the flow rate of the gas reactant,and M is the molecular weight of the gas reactant, whereby thepolymerized film has a thickness of 3 to 800 Å and a contact angle withwater in the range of from 100° to 130°.
 2. The magnetic recordingmedium of claim 1 wherein in the plasma-polymerized topcoat film, thefluorine-to-carbon atom ratio being from 0.3:1 to 2:1.
 3. The magneticrecording medium of claim 1 wherein the plasma-polymerized topcoat filmcomprises carbon, fluorine, and hydrogen, the carbon-to-hydrogen andhydrogen-to fluorine atom ratios being from 2:1 to 8:1 and from 0.2:1 to1:1, respectively.
 4. The magnetic recording medium of claim 1 whereinthe metal thin film magnetic layer predominantly comprises cobalt and atleast one optional member selected from the group consisting of Ni, Cr,and P.
 5. The magnetic recording medium of claim 1 which furthercomprises an undercoat layer between the substrate and the metal thinfilm magnetic layer.
 6. The magnetic recording medium of claim 1 whichfurther comprises an intermediate layer of a nonmagnetic metal disposedcontiguous to the surface of the metal thin film magnetic layer on theside of the substrate.
 7. The magnetic recording medium of claim 1 whichfurther comprises a protective layer of a nonmagnetic metal between themetal thin film magnetic layer and the topcoat layer.
 8. The magneticrecording medium of claim 5 wherein the undercoat layer has an irregularsurface.
 9. The magnetic recording medium of claim 1 which furthercomprises a protective layer of carbon between the metal thin filmmagnetic layer and the plasma-polymerized film.
 10. The magneticrecording medium in any of claim 1, 2, 3, 4-8 or 9, wherein the topcoatlayer additionally comprises hydrogen.